There have recently been an increased number of 2.95 bleed system failures, whereby the 2.95 bleed valve stays open above bleeds closed power. At high thrust operation this results is continuous hot, high pressure air impinging on the thrust reverser translating sleeve inner surface. The result can be a severe delamination of the translating sleeve and, in some cases, burnthough of the sleeve. There is evidence that this damage can occur after one flight with the bleed open.

Additionally, with the 2.95 bleed open at high thrust, hot high pressure air can eventually cause the seal between the bleed exhaust duct and the nacelle to deteriorate and leak. Hot air can enter the nacelle and cause abnormal engine indications potentially leading to in-flight shutdowns. There is evidence that an in-flight shutdown can happen during the first flight that the bleed is open.

Because of differences in nacelle design, reverser damage has been isolated to Airbus and McDonnell Douglas aircraft. Reverser damage is typically discovered during the preflight inspection of the aircraft. In-flight shutdowns tend to be isolated to Boeing aircraft due to bleed seal leakage, without associated reverser damage.

The purpose of this letter is to suggest a temporary engine operational check after engine start-up. The check is designed to make the pilot aware of the 2.95 bleed being open, and return the aircraft to the gate for maintenance action which should preclude reverser damage. It should be noted that qualified maintenance personnel will be required to check the function of and/or repair the bleed.
 
 
 
 
 

The purpose of the procedure is to detect a 2.95 bleed system malfunction after both engines are started to return to the gate for maintenance action and avoid a possible IFSD. The procedure is based on the EGT increase seen by the failure engine.

The procedure is as follows:

- After both engines are started with the engines at stabilized idle, calculate and record the difference in EGT between engines, this difference will take into account the different grade of deterioration of the engines.
Note: The 2.95 bleed valves must be closed at idle.

- At the next start and stabilized idle, calculate and record the difference in EGT between engines. If this difference has changed by 15 degrees C relative to the difference of the previous flight, return to the gate.

As you can see, the only data that should be recorded is the difference in EGT between engines and not the EGT of each engine.

Let’s make and example:
- First Flight:
EGT No. 1 = 440 C EGT No. 2 = 460 C
Difference in EGT = 20 C
This difference takes into account deterioration of each engine.

- Second Flight:
EGT No. 1 = 460 C EGT No. 2 = 485 C
Difference in EGT = 25 C
Difference change = (25 - 20) = 5 C. NO ACTION REQUIRED.

- Third Flight:
EGT No. 1 = 450 C EGT No. 2 = 500 C
Difference in EGT = 50 C
Difference change = (50 - 25) = 25 C. RETURN TO THE GATE AND TAKE APPROPRIATE MAINTENANCE ACTION SINCE THE CHANGE IS MORE THAN 15 C.
 
 
 
 
 

The attachments to the reference and all operators letter FLTOPS/72-00/DML: 6-05-05-1 provided an after start check for the pilots to determine if the engine 2.95 bleed(s) are open. This wire provides detail in an effort to obtain more consistent data for the check.

There have been complaints from several airlines about the subject check. We reviewed it with several attendees at the recent PW4000 conference in Zurich. We have obtained some results/data from two airlines, and are waiting for more information in an effort to determine possible modifications to the present method. Our goal is to provide a reliable/repeatable check of the 2.95 bleed.

Along with some inconsistent/unreliable results, we have seen some consistent data from the check. This leads us to believe, that a reasonable check is possible. At this time we can make the following comments. Our plan is to continue to keep you informed as more information becomes available.

At this time the primary problem with check seems to be recording EGT data when the engines(s) are not stable. This is a consequence of the pressures on the pilot to get the aircraft away from the gate as soon as possible.

First it is important to allow the engines to stabilize at idle after start. This is required by the start procedures of the various airplanes. The crews should be reminded that, during engine start, stabilized idle is not reached when the starter air valve closes, or when EGT reaches a peak value. An exact time period to wait for stabilized idle is impossible to provided because of the many variables that affect the start, but waiting for N2 to become essentially constant is a good guideline. This could take an extra 10 to 20 seconds after the rapid N2 acceleration of the start is complete.

When the last engine started is stabilized, the after start procedure is performed, now, another pause is needed to allow the engines to react to the loads imposed during the after start procedure. Again an exact time period to wait can’t be provided. Another 10 to 20 seconds is needed. It is suggest that the EGT data for the check be recorded as late as possible (without delaying taxi), after the after start procedure, before advancing the throttles for taxi.

There may be times when it is not possible to get stable data. The goal is to the 2.95 bleed check every flight, but it’s better to not do the check, than it is to record poor data. If the pilots feel it’s impossible to allow the time to stabilize the engines before recording EGT data, don’t do the check. The check can be done on the next flight, if possible, and compared to the most recent check.

Finally, this check is not mandatory, it is suggested for airlines who might find it helpful considering their own operations and experience.