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correlation between events is not possible, but in the aggregate, extra thrust increases the
aircraftÕs ability to avoid ground contact in the event of wind shear (See Appendix A).
4 AirmanÕs Information Manual para 7-1-21.
5AirmanÕs Information Manual para 7-1-23. MICROBURSTS
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5.3.1 The Effects of Additional Thrust in Windshear Recovery for the Airbus A- 320
(Takeoff)
This test was conducted as an evaluation of the effects of two different engine models on the
performance of the A-320 during the takeoff event with windshear. Of interest was the
performance in respect to altitude loss, airspeed decay, and time to climb out of the windshear
area. The two different engine models were the PW 2522 engine and the PW 2524 engine.
The data at attachment three shows the positive effect of extra thrust during windshear
recoveries. On average, the aircraft will lose 100ft less, 13KIAS, and spend approximately the
same time in the windshear event (0.5 sec delta). As windshear is a random event a direct
correlation between each event is not possible but in the aggregate extra thrust increases the
aircraftÕs ability to avoid ground contact in the event of windshear. Increased thrust also
reduced the amount of time the aircraft was exposed to the low altitude windshear event. This
reduction in time enables the aircraft to gain altitude quicker and thus avoid ground impact.
The amount of difference between the two engine models in recovery altitude and airspeed
loss is on the order of 20% of the total loss. The difference between the engine thrust output
is on the order of 10%. Thus a small increase in thrust results in a doubling of the safety
margin. If increased thrust is available it should be used to increase the safety margin. If the
aircraft is structurally able to have an increased thrust engine it should be installed. If the
reduced thrust option is desired for cruise cost reasons the pilot should be able to select the
higher thrust in an emergency situation. An increase in 20% in the safety margin prior to
ground impact is an obvious benefit.
5.3.2 The Effects of Additional Thrust in Windshear Recovery for the Boeing B-777 (Takeoff)
This test was conducted as an evaluation of the effects of two different engine models on the
performance of the B-777 during the takeoff event with windshear. Of interest was the
performance in respect to altitude loss, airspeed decay, and time to climb out of the windshear
area with the PW 4000 engine (74000 lbs thrust) and the PW 4084 engine (90000 lbs thrust).
During the windshear model 4 events the PW 4000 engine configuration had on average a 380
ft altitude loss, an airspeed loss of 55 KIAS, and spent 13.5 seconds in the event. The PW
4084 engine configuration had an average 200 ft loss, an airspeed loss of 51 KIAS, and spent
12.5 seconds in the event. For this windshear model, a 21% increase in thrust resulted in an
almost 100 % increase in performance
During the windshear model 2 event the PW 4000 engine configuration had a 36 KIAS loss and
spent 15.5 seconds in the event. The PW 4084 engine configuration had a 34 KIAS loss and
spent 11.0 seconds in the event.
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5.3.3 The Effects of Additional Thrust in Windshear Recovery for the Boeing B-777
(Approach)
This test was conducted as an evaluation of the effects of two different engine models on the
performance of the B-777 during windshear recoveries on approach. Of interest was the
performance in respect to altitude loss with the PW 4000 engine (74000 lbs thrust) and the
PW 4084 engine (90000 lbs thrust).
On average the PW 4074 (74,000 pounds thrust) engine configuration had a 233 ft altitude loss
with a min airspeed of 97 KIAS during the recovery. The PW 4084 engine (90,000 pounds
thrust) had a 185 ft loss with a minimum airspeed of 100 KIAS.
The test results show the positive effects of additional thrust during wind shear recoveries.
On average, the aircraft will loose 60 ft less.
5.4 Conclusion
Pilot authority to manage engine thrust to the maximum attainable level when required by
emergency circumstances must be provided. Reduction of the maximum attainable engine
thrust by FADEC systems must not be made for merely economic considerations. Although
routine or normal maximum available thrust may be set to a particular predetermined lower
value for operational considerations, a method to over-ride this restriction and obtain
maximum thrust available, consistent with aerodynamic and controllability issues, must be
provided.
6.0 FLIGHT ENVELOPE PROTECTIONS
The design goal of flight envelope protections is to protect the pilot and the aircraft from
exceeding the structural or aerodynamic flight envelope. The protection features afforded by
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