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AIRCRAFT - Different entry g levels were evaluated, pulling up to a target pitch attitude of
17.5 degrees. At the higher g levels, precisely matching the pitch attitude at 17.5 was
difficult, and would often result in a pitch overshoot of 2-3 degrees. The best run appeared to
be run 3, where at the end of the run, pitch was exactly at 17.5 degrees, which was right at the
pitch limit indicator (PLI), which is the threshold for stick shaker activation. Minimum
altitude loss below the pull up altitude (10,000 Ô) was observed to be about 100 feet on run 3.
On run 7, a near maximum performance pull up to 30 degrees nose high was executed,
activating the stick shaker. The airplane stagnated in climb at 10,900Õ and 105 kts with full
thrust. While this run gave the maximum initial pitch rate, it bled off energy rapidly, resulting
in complete loss of climb performance after a 900Õ altitude gain. During all of these
maneuvers, maximum thrust was applied at the beginning of the pull up. It nominally took 3-
4 seconds for the engines to come to full thrust, which usually occurred at about 15 deg nose
during the maneuver.
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Conclusions
The evaluation team preferred the flight envelope limiting features (Òsoft limitsÓ) of the B777
design to a Òhard limitÓ design. This was a subjective judgement based on the premise that
there may be situations unforeseen by the designers where the pilot might need to achieve full
aerodynamic capability as opposed to being software/control law limited.
V. Lessons Learned
A. Simulation
1. The use of an engineering simulator was beneficial in developing recovery
techniques and assessing the ability to perform the recovery maneuver without
overstressing the aircraft. This was very necessary in the build up phase to
avoid or assess the potential for damage to the test aircraft.
2. The use of fixed based simulators did not provide any motion cues and thus
was not a true simulation of the dynamics of the aggressive maneuvers being
tested or developed. A Òquick lookÓ evaluation was performed with a full
motion Airbus A-320 and a Boeing 777 simulator at the United Airlines Flight
Center, but these simulators did not have the necessary data acquisition
capability required for the test program.
B. Aircraft Flight Test
1. It was difficult to consistently obtain a pitch rate of 3 degrees/second over a variety of
airspeeds without considerable practice and finesse (both aircraft have a long moment
arm and there is no cockpit indication of pitch rate). The pitch rate attained at higher
airspeeds (250 to 300 KIAS) tended to be underestimated by the pilot. The evaluation
pilots felt that specifying a pitch rate of 3 degrees/second for line operations without a
parameter display is impractical. The motion cues and g onset rates played a very
important role in the closed loop performance.
2. Flight time to perform the evaluation was very limited. Because of this, detailed
coordination preplanning and performance were required to achieve the test
objectives.
3. Some of the coordination was international and this contributed to the communications
difficulties. Some final issues could only be raised and resolved face to face and this
resulted in some significant, last minute changes to the test card.
4. Flexibility in the test was required since our evaluators had limited control of the
aircraft configuration and test cards.
5. Last minute test constraints due to structural safety concerns raised during the flight
briefing required last minute modifications to the test cards. Care had to be taken to
maintain like maneuver comparisons in spite of last minute maneuver modifications.
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C. General
1. Manufacturer and FAA test pilots and purchasing company management pilots have
traditionally evaluated most aircraft. The Airline Pilots Association has played more
of a minor role in such evaluations until recently. Members of ALPAÕs APEC
Committee have evaluated virtually every transport aircraft in current use or
development and bring this broad aircraft knowledge along with considerable
operational experience to the evaluation process. As a result of APECs evaluation of
the CFIT recovery procedure for FBW aircraft, one major US airline, United Airlines,
has changed their CFIT recovery procedure.
2. New aircraft should require an OT&E phase where old procedures are evaluated in
light of new technological features. This may prevent the application of outdated
Standard Operating Procedures that are not in keeping with the benefits derived from
system improvements and advancements, such as FBW flight control systems.
　
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