High speed trim with flaps down, 737

[raspberry]

When you lower the flaps on the 737 the trim motor gives you a higher trim speed. If this is not working correctly, ie slow trim with the flaps down, is this a go or a no go item? I could not find any reference to this problem in the MEL, also the engineer looked puzzled.

[john_tullamarine]

... the trim motor gives you a higher trim speed

I'm really quite confused .. what does the trim motor have to do with trim speed ? and why would you want a higher trim speed with greater flap deflection ?

[BOAC]

JT - it is the speed of Stab TRIM movement that is referred to (ie 'trimming speed' rather than 'trim speed':) ). Faster with flap extended.

[john_tullamarine]

ah ha ! .. thank you, good sir ... jargon can be such a bore at times ..

[Mad (Flt) Scientist]

Not only is it, as ASFKAP mentioned, legally a "No Go" item if it isn't in the MEL, but from an engineering and safety perspective it should be a "No Go" also: you have something wrong with your stab system (whether the motor or the control unit) and that's hardly a trivial system.

The higher trim motor rate when flaps are down/in motion is presumably because it's required, so you may not have the requisite amount of handling. If your aircraft has a flap/stab interconnect, chances are the trim command in response to flap motion is for a number of seconds, not for an actual stab change, so if the rate is wrong, you'll get the wrong amount of stab as a result.

You also don't know if anything else is kaput in the stab system. Inflight would be a bad time to find out.

[I-2021]

is this a go or a no go item? I could not find any reference to this problem in the MEL, also the engineer looked puzzled.

Hello raspberry,

how did you find out that the high speed trim was not working ? Usually you set the T/O trim unit in the preflight procedure and you have flaps up. Did you recognize the problem in the after landing scan while reseting the trim with flaps not up ?

[raspberry]

I recognized the problem in the climb out and on the approach at the other end. As I could not find the problem in the MEL I grounded the aircraft.

[I-2021]

I see, and it was the same with the A/P On and Off ?

[raspberry]

yes it was the same with the AP switched on.

[I-2021]

Ok, thanks for your feedback !:)

[IFixPlanes]

For information only:
http://img177.imageshack.us/img177/5837/stabilizertrimcontrolcijd4.th.jpg (http://img177.imageshack.us/my.php?image=stabilizertrimcontrolcijd4.jpg)