|
|
10 Tanker DC-10 |
Evergreen B-747 |
Written by: |
Reviewed by: |
Tim Cox |
Steve Jacobsen |
Tom Bunce |
Jennifer Cole |
Matt Graham |
Tony Ginn |
Frank Batteas |
Chris Miller |
Tony Chen |
Tom Horn |
David Klyde |
Bob Lockyer |
Joe Sobczak |
Terry Rager |
|
Chris Miller |
This report, delivered under Modification 2 to Interagency Agreement
SAA2-402113 between NASA and the U.S. Forest Service, has been approved
for public release.
TABLE OF CONTENTS
Section |
Page |
Table of Contents |
2 |
1.0 Executive Summary |
3 |
2.0 Introduction |
5 |
2.1 Background
|
5 |
2.2 Objectives
|
5 |
3.0 Technical Approach |
7 |
3.1 Airworthiness Evaluation Approach
|
7 |
3.2 Mission Compatibility Approach
|
7 |
3.3 Understanding Current Operations
|
8 |
4.0 Results |
10 |
4.1 DC-10 Airworthiness Results
|
10 |
4.1.1 Structural Evaluation Results
|
10 |
4.1.2 DC-10 Retardant Delivery System Results
|
10 |
4.2 B-747 Airworthiness Results
|
11 |
4.2.1 Structural Evaluation Results
|
11 |
4.2.2 B-747 Retardant Delivery System Results
|
11 |
5.0 Conclusions |
12 |
5.1 B-747 Airworthiness and Mission Compatibility Conclusions
|
12 |
5.1.1 Airworthiness Conclusions
|
12 |
5.1.2 Mission Compatibility Conclusions
|
12 |
5.2 DC-10 Airworthiness and Mission Compatibility Conclusions
|
13 |
5.2.1 Airworthiness Conclusions
|
13 |
5.2.2 Mission Compatibility Conclusions
|
13 |
5.3 VLAT Overall Mission Compatibility
|
13 |
6.0 Deployment Recommendations |
15 |
6.1 Recommended Pre-Flight Preparations
|
15 |
6.2 The Dispatch Decision
|
15 |
6.3 Retardant Delivery Profiles
|
17 |
7.0 Suggested Future Research |
19 |
8.0 Acronyms and Abbreviations |
20 |
9.0 Consulted Subject Experts |
22 |
10.0 References |
22 |
1.0 Executive Summary
The objective of this limited assessment was to evaluate the safety
and utility of the DC-10 and Boeing-747 (B-747) in the Aerial Retardant
Delivery role using best available data. Specific objectives associated
with this effort were to:
a. Verify the airworthiness of the DC-10/B-747 aircraft with the Aerial
Retardant Delivery mission environment and flight profiles.
b. Determine the mission compatibility of the DC-10/B-747 aircraft with
the Aerial Retardant Delivery mission environment and flight profiles.
c. Develop (if one/both aircraft are assessed as airworthy and compatible
with the Aerial Retardant Delivery mission) recommended operational
usage regimes, policies, and procedures for incorporation by USFS and
Department of the Interior (DOI)
All of these objectives were accomplished. To do so, NASA utilized data
provided by the customer, vendors, and other sources to analyze the performance,
handling qualities, systems, and structural suitability of the DC-10 and
B-747 as potential Very Large Aerial Tanker (VLAT) aircraft. Simulator
and – in the case of the DC-10 – in flight evaluations of
the aircraft during mission-representative tasks were performed. Based
on this analysis, conclusions and recommendations were developed and are
provided in Sections 5.0 and 6.0 of this report. Very brief summaries
are provided below.
AIRWORTHINESS: Both aircraft were judged to be airworthy in the configurations
under evaluation. These assessments were made based on review of supplemental
type certificate (STC) and retardant delivery system documentation, as
well as limited inspections performed on the DC-10 airframe and retardant
delivery systems. Long term fatigue-related structural life remains an
area in need of further study, but the test team concluded that the ongoing
USFS continuing airworthiness program (CAP) should enable adequate monitoring
of fatigue life issues.
MISSION COMPATIBILITY: It was concluded that VLAT aircraft are probably
compatible with the wildland fire suppression mission, provided that they
are used to supplement other aerial retardant delivery platforms rather
than replace them in all environments. Steep or rugged terrain, reduced
visibility due to smoke and ash, and situations where topography or other
factors result in irregularly-shaped delivery zones will affect any aerial
retardant delivery aircraft, but it is believed these scenario characteristics
will affect VLATs to a larger degree, and may preclude their effective
use for certain classes of fires, particularly those with small or irregularly
shaped delivery zones. Extremely rugged terrain will make setting up for
stabilized deliveries challenging, particularly where the pilot must judge
wingtip terrain clearance while maneuvering over irregular terrain for
setup. These conclusions are based on pilot comments generated during
multiple simulated deliveries using high-fidelity visual simulators over
various terrain types. Dispatch decisions will need to take these and
other factors into account.
USAGE RECOMMENDATIONS: The major recommendations for employment that
result from this study relate to required terrain clearance, the type
of terrain, availability of qualified lead planes, low-altitude maneuvering
limitations, and size and shape of the desired delivery zones. The analysis
suggests that for level or gently rolling terrain where level to slight
descents (< 6-7%) are required, VLAT-class aircraft could probably
be employed with few restrictions as long as they remained above 300’
AGL during the delivery. Power margins for this class of aircraft, even
considering the possibility of single engine failure during delivery,
may actually permit climbing deliveries over very gradual slopes of less
than 3 – 4 % grade, provided suitable egress options are available.
Usage in very steep or rugged terrain is not recommended unless deliveries
can be performed with minimal maneuvering, a lead plane is available,
and adequate terrain clearance is available at the wingtips as well as
on centerline. Until significant experience is gained on VLAT platforms,
at least 400’ terrain clearance should be maintained in this kind
of scenario, and a climb must be initiated before any turns. It was also
found that on-board systems like auto-throttles and combined use of both
radar and barometric altitude alerts could reduce pilot workload as well
as provide improved situational awareness. These findings are also based
on pilot comments generated during multiple simulated deliveries using
high-fidelity visual simulators over various terrain types, as well as
on direct observation of experienced aerial firefighting crews performing
both airborne and simulator retardant delivery runs.
More detailed discussion of these and other results are provided in
the remainder of this report.
2.0 Introduction
A brief background for this program is given in Sub-Section 2.1 while
objectives are provided in Sub-Section 2.2.
2.1 Background
The U. S. Forest Service (USFS) is evaluating the potential of employing
converted commercial B-747 and/or DC-10 aircraft for wildland fire fighting
in the Aerial Retardant Delivery role. These aircraft are termed “Very
Large Air Tankers”, or VLAT, by the USFS. The USFS has no previous
experience operating aircraft of this size, and wishes to develop a plan
to utilize these aircraft safely and effectively. However, neither the
USFS nor the Department of the Interior feels they possess the necessary
flight test related skills to develop this plan or to properly assess
the aircraft. Therefore, the USFS engaged the NASA Dryden Flight Research
Center (DFRC) (in conjunction with the Ames Research Center) to plan and
conduct an evaluation of the VLAT aircraft to provide the necessary data
to support the eventual development of a USFS VLAT implementation plan.
The NASA VLAT Operational Test & Evaluation (VOT&E) team included
simulator expertise provided by Ames’ Aerospace Simulation Research
and Development branch; Dryden’s Operations, Aerodynamics and Propulsion,
Dynamics & Controls, and Aerostructures branches; and contractor support
provided by Computer Sciences (CSC) Corporation, and Systems Technologies
Inc (STI). This report describes the methods used, the test results, as
well as the conclusions and employment recommendations that flow from
those findings.
2.2 Objectives
The primary objective of this assessment was to evaluate the safety
and utility of the DC-10/B-747 in the Aerial Retardant Delivery role.
Specific top-level objectives associated with this effort include:
- Verify the airworthiness of the DC-10/B-747 aircraft with the Aerial
Retardant Delivery mission environment and flight profiles.
- Determine the mission compatibility of the DC-10/B-747 aircraft with
the Aerial Retardant Delivery mission environment and flight profiles.
- Develop recommended operational usage regimes, policies, and procedures
for incorporation by USFS and DOI.
To support the USFS objectives and verify airworthiness of the aircraft,
NASA conducted inspections of contractor activities concerning structural
integrity, procedures, quality assurance, and unique systems. To determine
mission compatibility NASA analyzed handling qualities and performance
characteristics of large supertankers relevant to the fire-fighting role.
In addition to these activities the intended flight operations of the
airplanes were evaluated.
This report documents the approach, analysis, results, and conclusions
of NASA to meet airworthiness and mission compatibility objectives for
the use of large supertankers in the fire-fighting role. Based on the
analysis, recommendations to the USFS are provided regarding operational
usage, policies, and procedures for the deployment of these airplanes.
Future research work is also suggested.
back to the top
3.0 Technical Approach
This Section describes the approach to analyzing the airworthiness and
mission compatibility of large transports in the fire-fighting role. Structural
issues, as well as maintenance processes and procedures are addressed
in Sub-Section 3.1. Flight operations, performance, and handling qualities
issues are addressed in Sub-Section 3.2 and 3.3.
3.1 Airworthiness Evaluation Approach
The airframe airworthiness review focused on the FAA FAR parts that
provide the loads and structural analysis requirements for the two types
of VLAT aircraft considered. The two FAA FAR Parts reviewed were FAR Part
25 “Airworthiness Standards: Transport Category Airplanes”
and Part 26 “Continued Airworthiness and Safety Improvements for
Transport Category Airplanes”. Part 25 is used by the industry for
analyzing large commercial passenger and cargo aircraft. Part 26 establishes
requirements for support of the continued airworthiness of and safety
improvements for transport category airplanes. These requirements may
include performing assessments, developing design changes, developing
revisions to Instructions for Continued Airworthiness (ICA), and making
necessary documentation available to affected persons. Holders of type
certificates and supplemental type certificates similar to those that
apply to Aerial Tankers are bound by the provisions of Part 26.
VLAT aircraft operate differently from typical commercial aircraft by
spending a larger percentage of their flight time at low altitudes, where
gust levels are higher and more frequent. In addition, VLAT aircraft are
required to fly at low altitudes to drop fire retardants, often in mountainous
areas. This often requires them to maneuver more aggressively than passenger
and cargo aircraft. FAR Part 25 & Part 26 were reviewed to determine
if they provide the same level of airworthiness to VLAT aircraft as they
do for typical large transport aircraft.
The airworthiness of the retardant delivery systems themselves was also
evaluated along with aircraft maintenance and operations. The process
for performing these evaluations had three parts: First, retardant delivery
system documentation provided by the aircraft operators was reviewed to
provide familiarity with the basic system design. Second, where the opportunity
presented itself, an on-aircraft inspection of the actual system installation
was performed. Areas where airworthiness or safety might be in question
were noted. Third, the aircraft maintenance processes and procedures were
reviewed, as well as aircrew and maintenance training practices and documentation.
The results of these evaluations are presented in Section 4.
To conduct the airworthiness evaluation several resources were examined
including instruction, operating, maintenance, and flight manuals, experts
in the field, and other relevant material.
3.2 Mission Compatibility Approach
Three main elements are included in the mission compatibility evaluations:
aircraft performance, handling qualities, and operational usage. The evaluation
was performed in four phases.
The first phase consisted of interviews with current tanker pilots and
others familiar with current aerial fire-fighting operations, as well
as review of pertinent documents on the subject of aerial firefighting.
The second phase consisted of analysis of existing B-747 and DC-10 aircraft
performance data, with comparison to the performance of current air tankers
such as the P-3, to determine basic suitability of the aircraft for the
mission.
The third phase utilized full motion B-747 and DC-10 flight simulators,
to evaluate handling qualities, aircraft performance, and operational
processes and procedures. This phase used the simulators to evaluate a
representative sample of mission profiles and generate data that was used
to analytically determine key airplane parameters, and evaluate the operation
of VLAT class airplanes in various terrain and configurations.
The fourth phase consisted of flight observations in the candidate VLAT
aircraft. These flights were conducted with the DC-10 VLAT aircraft operated
by 10 Tanker and the lead plane normally used in their operations as part
of routine aircrew training/proficiency flights.
3.3 Understanding Current Operations
In order to gain a basic understanding of fire fighting operations with
the current generation of aerial tankers, the NASA VOT&E team conducted
multiple interviews with experts familiar with the mission. The team then
conducted separate interviews with operators familiar with the operational
capabilities of the VLAT class of retardant delivery aircraft. The results
of these interviews have been incorporated in Sections 4 – 7 of
this report.
The team also examined the Interagency Tanker Board “Multi-Engine
Air Tanker Requirements” dated 1998 as a benchmark for VLAT aircraft
mission compatibility and compared predicted and simulator performance
characteristics against those required by the IATB. Other references,
including studies of mishap rates and causes, FAA TFR procedures, information
on Fire Traffic Areas, and company Flight Manual Supplements were also
reviewed.
Other documents created for or by the Forest Service were also reviewed.
Previous flight qualities and stability and control studies were also
examined.
To support the operational analysis of VLAT class aircraft, simulator
sessions were performed to investigate a variety of operationally relevant
aircraft configurations and settings. Approaches and drops were flown
with variations in flap settings, restricted visibility, landing gear
deployment, and active or inactive auto-throttles. Where appropriate,
altimeter and airspeed reference settings were varied. A major component
to be evaluated was flying approaches in a variety of terrains, including
gentle hills and rugged mountains. Attacking simulated fires going up-slope
and down-slope with profile variations to match descent rates to the slope
of the terrain were also a part of the investigation.
Three basic retardant delivery evaluation tasks were established as
simulation tasks for the purpose of stressing the pilot-vehicle system.
The tasks were designed to be relevant to the fire-fighting mission, yet
challenging, so that potential undesirable characteristics in the pilot-vehicle
system could be identified and documented. The tasks included a nominal
straight-in approach with roughly 3-5% glideslope; a level off, and a
pass over a targeted fire line where retardant delivery was simulated
(Figure ?3.1).
Figure 3.1: Nominal Retardant Delivery Profile
4.0 Results
Note: These results are based on technical analysis of available aircraft
performance data validated where possible via simulator. In flight evaluations
of the DC-10 were also performed, and those results are documented here
as well.
Results fall into two categories. The first category is basic airworthiness
of the VLAT airframes and the retardant delivery systems as integrated
into those airframes. The second category is the operational compatibility
of this class of aircraft with the basic and/or specially tailored aerial
retardant delivery mission as envisioned. This report addresses the airworthiness
for each aircraft individually. It then discusses mission compatibility
for the VLAT class as a whole.
4.1 DC-10 Airworthiness Results
Structural evaluation, retardant delivery systems, and inspections and
maintenance evaluations for the DC-10 are provided in the following sub-sections.
4.1.1 Structural Evaluation Results
FAR 25.571 Damage Tolerance and Fatigue Evaluation of Structure require
“the typical loading spectra” be used in the analysis. This
should include the appropriate gust and maneuver loading magnitudes
and frequencies VLAT aircraft are going to experience. Furthermore the
gust levels stated in FAR 25.341 Gust and Turbulence Loads and Part
25 Appendix G “Continuous Gust Criteria” are altitude dependent.
For VLAT aircraft that spend much of their flight time in low altitudes,
this means higher gust level assumptions need to be used in the analysis,
which was done in this case. As always, such assumptions are only estimates,
so actual gust loads data captured via the CAP will be valuable in confirming
the structural analysis performed.
The recently released FAR Part 26 subpart E requires Type Certificate
and Supplemental Type Certificate holders to perform Damage Tolerance
Evaluation for alterations and baseline structures are affected by the
alterations. According to the Federal Register (Vol 72, December 12,
2007, DoT FAA Damage Tolerance Data for Repairs and Alterations), “…in
some cases, air carriers improperly classified repairs and alterations
that affect fatigue critical structures as “minor” and damage
tolerance evaluations were not conducted.”. With the newly created
FAA rules, Part 26 ensures damage tolerance evaluation is done for all
alterations.
4.1.2 DC-10 Retardant Delivery System Results
After examination of system documentation and explanatory discussions
with the operators, NASA engineers found the retardant delivery systems
to possess a suitable level of engineering design and redundancy.
4.2 B-747 Airworthiness Results
Structural evaluation, retardant delivery systems, and inspections and
maintenance evaluations for the B-747 are provided in the following sub-sections.
4.2.1 Structural Evaluation Results
See Section 4.1.1
4.2.2 B-747 Retardant Delivery System Results
After examination of system documentation and explanatory discussions
with the operators, NASA engineers found the retardant delivery systems
to possess a suitable level of engineering design and redundancy.
5.0 Conclusions
All three objectives were addressed and, in part, met.
The first objective, to evaluate the airworthiness of the VLAT Class
or aircraft, was too broad to completely meet in a limited test program.
Since the mission tasks are entirely within the normal flight envelope
of the aircraft, airworthiness can be assumed based on certification of
the aircraft. The simulator tasks showed that the required maneuvers could,
with some reasonable limitations, be conducted within the certified flight
envelope. Since the simulator was not quite “production representative”,
an unqualified statement about airworthiness cannot be made. However,
based on aerial fire retardant delivery simulations conducted in the simulators,
it can be stated that the aircraft exhibit no performance or handling
qualities short falls that would cause them to be non-airworthy in the
environment tested. We also concluded that they are basically suitable
for the mission, with some limitations. The testing conducted in this
program led to a preliminary evaluation of what those limitations might
be, and several limitations are suggested. Further testing and analysis
is needed to provide a comprehensive set of limitations for the VLAT Class
of aircraft.
The second objective was to determine compatibility of the aircraft
for the fire retardant delivery mission. Again, with limitations and further
testing/analysis required, the aircraft were found to be suitable for
the mission.
The final objective was to develop procedures for use of this class
of aircraft for this mission. The testing led to several possible procedural
recommendations that are discussed in Section 6. Again, more testing would
be needed to refine these ideas and make specific recommendations.
5.1 B-747 Airworthiness and Mission Compatibility Conclusions
The B-747 airworthiness and mission compatibility conclusions are presented
in the following sub-sections.
5.1.1 Airworthiness Conclusions
The team concluded that complying with FAA Part 25 and Part 26 (Damage
Tolerance Evaluation should be updated to Part 26 if it was completed
before Part 26’s release) should provide the same level of safety
for the VLAT aircraft as for regular commercial large transport aircraft,
provided suitable maintenance and inspection protocols are put in place.
The USFS CAP program designed for extensive, long-term structural monitoring
of these airframes should provide a suitable method to capture relevant
structural integrity data and enable operators to sustain these airframes
in an airworthy condition for the long-term.
5.1.2 Mission Compatibility Conclusions
Based on the limited simulator flight-testing conducted in this study,
the B-747 Supertanker was considered suitable for the USFS fire fighting
mission. Further testing should be conducted to refine the results of
the Phase II tests, and develop additional operational procedures and
techniques. Options for even better results include changes in airspeed
control procedures and possibly to flap settings in the drop zone.
5.2 DC-10 Airworthiness and Mission Compatibility Conclusions
The DC-10 airworthiness and mission compatibility conclusions are
presented in the following sub-sections.
5.2.1 Airworthiness Conclusions
The team concluded that complying with FAA Part 25 and Part 26 (Damage
Tolerance Evaluation should be updated to Part 26 if it was completed
before Part 26’s release) should provide the same level of safety
for large firefighting aerial tankers as for regular commercial large
transport aircraft, provided suitable maintenance and inspection protocols
are put in place. The USFS CAP program designed for extensive, long-term
structural monitoring of these airframes should provide a suitable method
to capture relevant structural integrity data and enable operators to
sustain these airframes in an airworthy condition for the long-term.
5.2.2 Mission Compatibility Conclusions
No adverse performance or handling qualities problems were observed
that would make the DC-10 unsuitable for the fire retardant delivery
mission. The generally pleasing handling qualities inherent in the DC-10
made the operational tasks relatively straightforward. The DC-10 flights
validated some findings from the simulator as both lateral and vertical
offsets and corrections were observed.
The NASA VOT&E team viewed the 10 Tanker operations for several
hours around their facility on 13 Nov 2008. The operation appeared to
be professionally run and manned by dedicated pilots, crew, and maintenance
personnel. The flights permitted the team to view the spotter aircraft
operation from inside the Lead Aircraft and also observe operations
from the flight deck of the DC-10 as they conducted several deliveries.
The accuracy of the drop appeared suitable for the planned mission.
5.3 VLAT Overall Mission Compatibility
Although the majority of operational task evaluations were performed
in the B-747 simulator, owing to the higher fidelity of the visual system,
a limited number of runs were also performed in the KC/DC-10 simulators.
As a result, the test team concluded that the VLAT class as a whole is
airworthy and compatible with the mission. Some specific compatibility
aspects are addressed in Table 5.1.
back to the top
Table 5.1: Mission Factor Compatibilities
Mission Factor |
Compatibility |
Remarks or Employment Considerations |
|
none |
partial |
full |
|
|
Required Infrastructure |
|
X |
|
May need added ramp area and specialized servicing equipment |
Deployability |
|
X |
|
See Above |
Lead Plane Requirements |
|
X |
|
Specially trained lead pilots will be needed during initial ramp-up |
Range/Endurance |
|
|
X |
|
Airspace Usage |
|
X |
|
May need special handling to avoid wake turbulence issues for others |
Terrain/Density Alt |
|
|
X |
|
Delivery Speeds |
|
|
X |
At top end of desired range |
Accuracy |
|
|
X |
When used in appropriate scenarios |
Coverage Levels |
|
|
X |
|
Reserve Performance |
|
|
X |
Excellent |
|
|
|
|
|
6.0 Deployment Recommendations
This section includes initial recommendations for usage based on available
data. Most recommendations are provided along with the basic rationale
for each.
6.1 Recommended Pre-Flight Preparations
- Recommended minimum equipment requirements: No changes are proposed.
Current operational procedures appear to be satisfactory.
- Changes to crew training to enhance safety and effectiveness: See
the recommended changes to delivery procedures in section 6.3 below.
- Changes or refinements to maintenance and inspection regimes: No
specific changes are proposed at this point, but it should be expected
that as data are captured under continued airworthiness program, operators
will be positioned to make appropriate adjustments to maintenance and
inspection routines to ensure long-term airworthiness.
6.2 The Dispatch Decision
- Terrain types and clearances based on available climb gradients with
1 engine out do not suggest more restrictive operational criteria than
existing aerial tankers or lead planes. There is actually higher performance
than existing tankers due to the proposed VLATs operating at a much
lower weight than their original design even taking into consideration
their slightly faster speed.
Recommendation: Temperature and pressure altitude conditions
that are suitable for other firefighting assets should prove more than
sufficient for a positive dispatch decision for the VLAT class of tankers.
- Terrain types and clearances based on available non-accelerating
descent gradients was not quantified in the limited time available in
the simulators, but it was apparent that these aircraft are low drag
optimized and do not provide a high non-accelerating descent rate without
the use of drag devices. This was not explored in the simulations. A
higher drag would also provide an extra margin of safety if the extra
drag could be reduced quickly by forcing the engines to be “pre-spooled”
at a higher thrust setting.
Recommendation: Delivery situations that require steeper than average
descent angles for a successful delivery may preclude use of the VLAT
class until suitable drag devices and usage procedures are proven.
- The VLAT class of aircraft is designed to handle the same approach
and landing wind and turbulence for their normal operation as the other
aerial tankers. The approach is currently flown in a similar manner,
with an extended low pass before executing a go-around. High altitude
airports are similar to high altitude fire locations with the exception
of the close proximity to trees and rugged terrain. This very important
difference is handled with the current procedure where the Lead Aircraft
flies a pass above the target drop height. This should be continued
in order to assess the turbulence and winds at a safe height, followed
by another pass at the expected drop height. The Lead Aircraft with
its lower wing loading will be more sensitive to conditions than the
VLAT and will call off runs that exceed safe operation. The extensive
experience of the aerial tanker crews are of prime importance to determining
safe conditions and staying within safe limits.
Recommendation: Maintain requirement for use of Lead
Aircraft whenever terrain is questionable, and avoid sending inexperienced
VLAT crews into steep or rugged terrain.
- Because the VLAT aircraft are operating at a weight that is approximately
half their maximum design gross weight, even a 2 G turn is well within
their performance capability. These aircraft have an excess of performance
that is not normally seen in passenger operations in order to provide
a very high level of comfort to the ordinary traveler. That performance
is rarely called upon to save the aircraft from danger, but is there
if needed. The impression that the VLAT aircraft are slow and not very
maneuverable comes from that standard operational experience where the
slow, slightly banked turn is the norm. Takeoff performance and the
steep climb angle that is obtained give some glimpse into what can be
expected when that performance is needed.
Recommendation: See item 1 above.
- Predicted delivery effectiveness, if used in accordance with recommended
procedures, is excellent and provides a wider and longer fire break
than the smaller aerial tankers. This is a new tool that will enhance
the existing fleet which would need to make multiple overlapping passes
to create the same line. Techniques will be developed as the firefighting
team learns the VLAT strengths and weaknesses. For example: where the
terrain is too steep for the VLAT to follow the contours, the smaller
tankers can overlap the line to complete the defenses with fewer drops
and therefore less time consumed by the turn around.
Recommendation: While VLAT aircraft have a good “partial load”
capability, their use when multiple disjointed drops are required should
be carefully evaluated for safety and cost-effectiveness prior to dispatch.
- The handbooks used by the firefighters to determine coverage levels
based on fuel and the flame length that an aerial drop is effective
against will need to be updated to include the capability of the VLAT
class of aircraft to lay a very wide, as well as long, line. The coverage
level 8 setting at the nominal drop height of 300 or 400 ft would be
reduced at higher drop heights, but would also be wider, with the ability
to slow the advance of fires with longer flame length. By making multiple
passes, the VLAT may actually be able to do this since it has a relatively
quick turn around time and a high flight speed or could make partial
drops in one sortie where current tankers would need to make many more
flights, or require more aircraft in the circuit. There simply could
be insufficient time available to create that kind of line before the
fire advanced.
Recommendation: See 5 above.
- Current limits for aerial tankers limit their use to clear visual
conditions for terrain and obstacle avoidance and should be followed
for VLAT aircraft. Simulation with 3 mile visibility was at the limit
of the ability of the pilot to make a successful approach to the drop
point. The simulation did not have a lead plane and the difficulty that
may pose to visually see the smaller aircraft against smoke plumes and
ground clutter, nor the advantage that a lead plane provides in showing
the VLAT where to fly, nor the sense of depth, detail, and wide field
of view that is available to a pilot flying in the real world.
Recommendation: Carefully consider the VLAT dispatch
decision if visibility is a factor.
6.3 Retardant Delivery Profiles
Both aircraft have developed good retardant delivery profiles and crew
coordination. The use of a Lead Aircraft on a single monitored frequency
reduces the chance of radio distractions and improves drop communication.
Crew coordination and division of aircrew duties are excellent.
The ride along with the DC-10 during practice runs was perhaps the most
beneficial of the tests. The team was able to observe first hand how they
used the procedures they developed for retardant delivery. Limitations
of the simulator did not include following a Lead Aircraft or a good visual
for changing terrain. The entire fire fighting mission hinges around being
at a delivery altitude that optimizes the fire retardant without compromising
the delivery aircraft. VLAT ridgeline crossings enroute or on exiting
may need to be constrained more than the typical 200-300 foot AGL altitude
minimum often used by current generation tankers.
Terrain clearance is visual with clearance based on pilot comfort. This
is hard to do in a simulator because the visual system is not made for
this mission. Despite the exceptional flying demonstration in the simulator,
the approaches crossing ridges seemed to be unconstrained – almost
overlooked – during the concentration to meet speed and altitude
on target. Large aircraft have larger wingtip and fuselage clearance requirements
and bear constant consideration. Everyone seemed to agree that this is
the one area with a potential for disaster or problem, especially if the
crew is distracted by reduced visibility, target fixation, or there is
an error by the Lead Aircraft. The current generation aerial tanker technique
of 30 degrees max bank angle at low altitude may be inadequate. Consideration
should be given to making altitudes slightly more restrictive to account
for the longer wing span of these aircraft. On those rare occasions when
they do have to fly lower than the delivery height above a ridge line
to set up for the drop, it is imperative that they be lined up for the
drop to avoid ridge-crossings while still in a banked attitude.
Recommendation: Develop terrain clearance guidelines
and training.
The aural warning (or similar) circuit breaker was pulled to eliminate
nuisance warnings during drops. This may silence all warnings, however,
and should not be done on the aircraft especially if forgotten to be reset
during return to base.
Recommendation: VLAT warning systems could be designed
so that nuisance warnings can be inhibited without disabling any other
warnings. Operational procedures and checklists should include the reactivation
of all warning systems prior to approach and landing.
Several runs were made with reduced visibility. When visibility was
lowered to 3 NM, the task became much more difficult. Misalignment with
the target required about a half mile for assessment, and correction to
the target drove up pilot workload significantly. Adequate performance
was achievable, but moderate or greater pilot compensation was needed.
When visibility was increased to 5 NM, the task became much easier. With
visibility at 10 NM, the visibility was almost not a factor at all. Experience
has shown that the simulator becomes more realistic as visibility decreases.
With the simulator, you may get poor height awareness in good visibility
daylight conditions, but as the visibility decreases through 3 NM and
the daylight gives way to night, the real world visual cues are very well
represented in the simulator.
Recommendation: Based on the simulator tests, 3 NM
should be the absolute minimum visibility required to attempt the mission.
7.0 Suggested Future Research
The following list suggests areas where future research may be warranted:
- Conduct limited flight test evaluations to:
- verify aircraft dynamics system identification and evaluation
maneuvers discussed here.
- investigate PIO potential for VLAT class airplanes
- Consider further simulation research with following objectives:
- evaluate the benefit in pilot workload and piloting performance
of incorporating a HUD that displays flight path marker, altitude,
speed, and heading. An option could be included to look at guidance
cues as well.
- evaluate the effect of a retardant dump on mission success using
a representative model of the change in aircraft dynamics and aerodynamics.
- define more rigorously the limitations associated with the lateral
offset delivery. This could potentially lead to a better recommendation
on how close to the drop area offset corrections can reasonably be
expected to be made. It also would put a higher demand on the pilot-vehicle
system, to see if the potential PIO tendency noted in the roll axis
is uncovered with an evaluation task.
-
Better characterize the mountainous turbulence and wind profiles
for testing aircraft against and simulation training of aerial tanker
pilots.
-
Collect simulation data to characterize the altitude vs airspeed
trade-off with an engine failure and the time required for spool up
against a more realistic terrain visual system.
-
Determine what percentage of the potential fire scene is off limits
due to terrain gradients and the VLAT aircraft’s ability to
fly non-accelerating decent profiles into the drop zone and climb
out of a single engine failure scenario. An interactive map with varying
approach directions and with the ability to show different aircraft
types that can handle that terrain could be created for field use
to help make the decision on where to create a fire break, and what
aircraft to deploy. Integrate this with the existing maps that are
fed data from IR sensor aerial platforms.
-
Investigate flow-shaping surfaces to direct more of the water or
retardant down and away from the aircraft upon release. This could
also help reduce maintenance issues with corrosion on the aft fuselage
where retardant is caught in the standard airflow.
back to the top
8.0 Acronyms and Abbreviations
AFFTC – Air Force Flight Test Center
AGL – Above Ground Level
ARC – Ames Research Center
ARD – Aerial Retardant Delivery
CAP – Continued Airworthiness Program
DFRC – Dryden Flight Research Center
DOI – Department of the Interior
DOP – Dryden Operational Procedure
FAA – Federal Aviation Administration
FAR – Federal Aviation Regulation
FFT – Fast Fourier Transform
FREDA – FREquency Domain Analysis
HQR – Handling Qualities Rating
ICA- Instructions for Continued Airworthiness
KIAS – Knots Indicated Airspeed
LLC – Limited Liability Corporation
MSL – Mean Sea Level
NASA – National Aeronautics and Space Administration
Nz – g-loading (z axis)
PID – Parameter IDentification
PIO – Pilot Induced Oscillation
PRV – Pressure Regulating Valves
PSD – Power Spectral Density
RW – Runway
STC – Supplemental Type Certificate
STI – Systems Technology, Inc.
TBD – To Be Determined
USFS – United States Forest Service
VLAT – Very Large Aerial Tankers
VOT&E – VLAT Operational Test & Evaluation
9.0 Consulted Subject Experts
Telephone or face-to-face interviews were conducted with a number of
experienced aerial firefighting personnel. Interviewees included:
Jack Maxey – 10 Tanker
Brian Lash – Butler Aircraft
Cliff Hale – Evergreen
Walt Darran – CalFire
Dennis DeGeus – 10 Tanker
Phil Johnson – CalFire
Pat Norbury – USFS
Scott Fisher – USFS
Greg House – USFS
Rick Hatton – 10 Tanker
10.0 References
- “Instructions For Continued Airworthiness, 10 Tanker STC, LLC
DC-10, Chapter 2, Fire Fighting System Description”, Report No.
2547, Aircraft Technical Service, Inc., 11/21/2005.
- “Commercial Operations Manual, Chapter 7, Flight Maneuvers and
Techniques,” 10 Tanker LLC.
- “DC-10 Maintenance Manual, Revision 80,” McDonnell Douglas
Corporation, 1/1/2004.
- “FAA Approved Airplane Flight Manual Supplement to the Boeing
747-200C Airplane Flight Manual for Evergreen International Airlines,
Inc. Air Tanker Modification,” Evergreen International Airlines,
Inc., 10/27/2006.
- “B-747 Aircraft Operating Manual,” American Airlines Flight
Department, 1983.
- E-mail correspondence with Rick Hatton, 10 Tanker LLC.
- E-mail correspondence with Cliff Hale, Evergreen International Airlines,
Inc.
- “Airtanker Drop Test Report, Evergreen Supertanker Tanker 947,”
USDA Forest Service, 8/10/2006.
- “Section III – Multi-Engine Airtanker Requirements (2006
and forward),” Procedures and Criteria for the Interagency Airtanker
Board (IAB), July 2006.
- “Section VII – Tank System Criteria,” Procedures
and Criteria for the Interagency Airtanker Board (IAB), July 2006.
- Johnston, J.P., “Interagency Airtanker Board - Charter, Criteria,
and Forms,” USDA Forest Service - National Interagency Fire Center,
9857 1803-SDTDC, July 1998.
- Veillette, P. R., “Crew Error Cited as Major Cause of U.S.
Aerial Fire Fighting Accidents,” Flight Safety Digest, Vol. 18,
No. 4, April 1999.
- USDA Forest Service Briefing; “What is a Fire Traffic Area?”,
May 2003.
- Fire Traffic Area (FTA) kneeboard and poster depiction, March 31,
2006.
- “Boeing 747 Model 747-123 Operations Manual Volumes II and III,”
The Boeing Commercial Airplane Company, Seattle, Washington, March 1978.
- “Raytheon Aircraft Beech Super King Air 200 & 200C Pilot’s
Operating Handbook and FAA Approved Airplane Flight Manual,” Raytheon
Aircraft Company, Wichita, Kansas. Revision A13, January 2002.
- “USAF Series KC-10A Aircraft Flight Manual Performance Data,”
USAF TO 1C-10(K)A-1-1, October 1993.
- “USAF Series C-130A, C-130D, C-130D-6 Airplanes Flight Manual
Appendix 1 Performance Data,” T.O. 1C-130A-1-1, January 1980.
- “Lockheed P-3C Flight Manual,” NAVAIR 01-75PAC-
- “FAA Approved Airplane Flight Manual Supplement to the Boeing
747-200C Airplane Flight Manual for Evergreen International Airlines,
Inc. Air Tanker Modification,” Approved October 27, 2006.
- Interagency Aerial Supervision Guide 2008.
- Fisher, S., “Continued Airworthiness Program – CAP,”
U.S. Forest Service Presentation.
- Payne, B., “DC-10 Supertanker Operating Plan,” CAL FIRE,
Revision 5, August 2, 2007.
- “Summary of Comments Received in Response to USFS Proposed Continued
Airworthiness Program (CAP),” In Fedbizzops (SN-2007-07), July
10, 2007.
- “Very Large Airtanker Drop Height Considerations”
- “USDA Forest Service Airtanker Drop Test Report - Evergreen
Supertanker - Tanker 947”
- Nelson, J., “US Forest Service Operational Loads Monitoring
Program,” PowerPoint Presentation, 11th Joint FAA/DoD/NASA Aging
Aircraft Conference, Phoenix, AZ, April 22, 2008.
- Manson, A. L Lt and Traskos, R. L.; “Final Report - Flying
Qualities and Performance Technical Evaluation of the P-3B Airplane,”
Naval Air Test Center, FT-98R-68. 31 Dec 1968.
- “Combined Stability and Control and Aircraft and Engine Performance
Trials of the P3V-1 Airplane,” Naval Air Test Center Technical
Report, FT2122-020, May 6, 1963.
- “Turbulence Researchers Working on Detection Systems,”
30 November 1999 http://www.usatoday.com/weather/wturb497.htm
- Atmospheric Properties Calculator based on US Standard Atmosphere
1976. http://www.aerospaceweb.org/design/scripts/atmosphere/
back to the top
|
|