[1-19通用] 关于QRH与MEL的区别

Q：

There are two cowl anti-ice indications for each engine.One is TAI indication on CDS,another is COWL VALVE OPEN lights on the anti-ice panel.

Refer to QRH NNC 3.2 for COWL VALVE OPEN.Why are there no steps to verify that another indication is normal when there is only one abnormal indication?

A：

The ENGINE COWL VALVE OPEN OR TAI INDICATION NNC condition statement reads:

"One or both of the following occurs:

-An engine COWL VALVE OPEN light stays illuminated bright blue

-An amber TAI indication is shown."

Note the use to the phrase "one or both". The purpose of the checklist is to safely operate the airplane with a failed cowl anti-ice valve. Only one of the two possible indications is required to determine that the valve is failed and the checklist should be performed. The checklist is not intended to troubleshoot the cowl anti-ice valve indicating system, thus there are no steps to identify and incorrect indication. The crew should regard any cowl anti-ice valve failure indication as valid.

Q：

I have another questions for MMEL 21-21-02-01,Flight Deck Temperature Control Systems,Primary / Back-up Modes for 737-800, Installed quantity is two and required quantity is one.

The OPERATIONS(O) procedure is used to verify normal operation of the remaining flight deck temperature control system (Primary or Back-up).

But if both the Primary and Back-up Modes are INOP and the left pack temperature control systems is normal,still this OPERATIONS(O) procedure will passed.

A：

The (O) procedure in MMEL/DDG 21-21-02-01 assumes that maintenance has done troubleshooting to verify that either the primary OR back-up mode is inoperative. If maintenance determines that both the primary AND back-up modes are inoperative then MMEL/DDG 21-21-02-02A or 21-21-02-02B would be used for dispatch and not MMEL/DDG 21-21-02-01.

Q：

Refer to the SDS 21-60-00,a failure of the ram air temperature sensor or interface,or ram air door actuator or interface will causes the PACK light to come on only when the master caution system is recalled and will extinguish when reset.

In this condition,can we use DDG-21-32?or we must use DDG-21-05.

For my point,the DDG-21-32 is for Pack Temperature Control System,if the fault code is RAM AIR in PZTC bite,we can not use the DDG-21-32 to dispatch the airplane even if the AIR COND and associated PACK light can extinguish when Master Caution reset.That 's because the the ram air temperature sensor and ram air door actuator belong to the Pack Ram Air Systems and not the Pack Temperature Control System.

A：

The appropriate 737 MMEL/DDG item is 21-05 when the ram air system is determined to be the source of the fault. The Boeing Fault Isolation Manual (FIM) is the first reference to be used for determining what has caused a fault to appear. The FIM information is then used to determine what repair should be undertaken and/or what dispatch relief to pursue. Although the Aircraft Maintenance Manual (AMM) provides excellent system description information, it is not intended for use in diagnosing a problem. As you noted, if the FIM had identified the Pack Temperature Control System as the cause for a PACK Fault to annunciate, then MMEL/DDG item 21-32 would be available for dispatch relief if all the provisos are met.