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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.
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Attachment One
Engine Thrust Models
On File
Attachment Two
UAL Standard Operating Procedures
Excerpt Ð Ground Proximity Warnings
On File
Attachment Three
Windshear Recovery Data Sheets
On File
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Evaluation of Engine Effects on
Takeoff Performance in Windshear
in the B-777
Harry Walker
United Airlines
28 Jul 1998
Revision 14.0 33
I. Overview
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).
II. Equipment Description
The evaluation was conducted on the B-777 simulator number two at UAL DENTK. It
contained all aero models for the B-777 as well as being fleet representative of the current
UAL fleet.
III. Data Acquisition
F/O Harry Walker and Mr. Bill Dobbs (DENTK Sims) conducted the evaluation. The
simulator was placed at a representative gross weight (approx. 499,500 lbs.) and in position
on the runway. A normal takeoff was performed and the autopilot was engaged shortly after
the gear was retracted. All data was collected with the autopilot on to eliminate pilot
technique from the windshear recovery. Test conditions were standard day, gear up prior to
windshear, flaps 5. Two different windshear models were used. Windshear model 2 and 4.
Model 2 has a windshear event occur at approximately 55 feet AGL. Windshear model 4 has
the windshear event occur at approximately 550 feet AGL. Four event sets were flown. Set
One with the PW 4000 engine, windshear model 2. Set Two with the PW 4000 windshear
model 4. Set Three was with the PW 4084 engine with windshear model 2. Set Four with the
PW 4084 engine with windshear model 4. All events were flown with the autopilot effecting
the recovery. Once windshear was detected (start of airspeed loss) the TOGA button was
pushed twice and the throttles pushed to maximum and held there to eliminate any
autotthrottle tendencies to reduce thrust. The simulator windshear recovery-training program
automatically generated data at attachment one.
IV. Findings / Results
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.
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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Windshear Model 4 Windshear Model 2
Averages PW 4000 PW 4084 PW 4000 PW 4084
Alt Loss 380 ft 200 ft None None
Airspeed Loss 55 KIAS 51 KIAS 36 KIAS 34 KIAS
Time in Event 13.5 Sec 12.5 Sec 15.5 Sec 11.0 Sec
V. Conclusions / Recommendations
The data at attachment one shows the positive effect of extra thrust during windshear
recoveries. If increased thrust is available to the pilot it should be used to increase the safety
margin. 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.
Attachment One
Takeoff Events with Windshear
B-777 Data Sheets
On File
Revision 14.0 35
Evaluation of Engine Effects on
　
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