737 trim wheels

[xfeed]

Can anyone tell me why the left-hand trim wheel and the right-hand trim wheel on the flight deck are made by two different manufacturers? Is this true for other planes besides the B737?

Cheers!

[Earthmover]

Well I never knew that, and I've been watching them clatter round for some thousands of hours!

Could it be that major manufacturers adopt a belt and braces approach? - one component supplier has, say, production difficulties, so to stop a trim wheel holding up the production line, you order 'em all from the other supplier.

[Herod]

Earthmover, nice to see you're still active on the forums !! I didn't know it either, but you explanation seems as good as any. "The future's in the stars"

[alexban]

I never knew that but I'll check today.One other question though,why it's a difference between stab trim position between left or right seat adjustment?.
When you set for ex 5 units trim from the capt seat,it will be aprox 4.7 on the F/O scale.
I think I saw this on all 737's I flew with.
Alex

[Earthmover]

Well hello Herod! Glad to see we're both still alive.

Sorry Alex, I must have a 'rogue' 737 - happened to check this today, and we both had 5.1!! :D

[4MONU]

Alexban - good observation.

I confirm the same! I have also noticed that on all the 737's (right from the jurrasic's, classic's & NG's) - all have 'some' difference between the left & right trim readouts. I have noticed it on brand new A/c's also, just delivered from Boeing. Earthmover - you must have flown a super-rigged A/c !

I remember - as a F/O, we used to reach over to set it as per the Capt's readout, least we tick off the old man !!

The explaination I have gathered over the years is:

All calibration is done as per Left side trim readout. If you look even more closely - you will notice that there is even a difference between the length of scale between left and right. i.e. length of scale from 1 to 15 units, is longer / shorter than the other. (now my old age has made me forget which side !!). This is easily done by making small marks on a piece of paper and comparing left and right!! There is also a difference in length in of the opening in which the pointer runs. Also decals are different.

The engineers need to get the left and right trim wheels between a certain MM value during calibration, and since I believe this is a very cumbersome process, most guys just make sure its withen the value, and not perfect ! Can also tell you, that the DFDR pick-up is from the left side, but not necessary the same as what the pointer shows.

Have questioned a few Boeing test pilots and safety pilots, but did not get favourable answers.

X-feed. I am not aware that 'only' different manufactures make left and right trim wheels. If it is true, then its a VERY good question, and then I'm sure it will have a very GOOD reason.

Sorry for the long post.

4MONU

[alexban]

xfeed: you must be an engineer,cause I've looked at the trim wheels ,and couldn't find the manufacture numbers. There are some numbers on the inside of the wheel,but you have to dismantle it to see that nr.And I've seen no manufacture name on the wheels.
Brgds Alex

[xfeed]

ASFKAP,

I got my information from a 737-300 video of a GO flight from Stanstead to Lisbon. The plane had just been delivered (this was 1999) from Seattle two days before the flight and the captain (who was the chief pilot for GO at that time) says, during the flight, that "an interesting fact about the trim wheels is that the left-hand one and the right-hand one are made by two different manufacturers." Unfortunately, the good captain didn't say WHY they were made by different manufacturers. I was just curious so I'd thought I'd ask the pros.

I appreciate the responses.

Cheers!

[???pax]

I believe tht chap who made that statement is a ppruner going by the name of "Hamrah".

[xfeed]

???pax,

I do believe you are correct. I looked at his profile and his name came up.

So, if Hamrah is reading this...let me first say that I love the video; thanks for agreeing to do it. You were very thorough in explaining all the systems and got me more interested in the 737. Perhaps as the chief pilot (at that time) you know something about these trim wheels that others are not aware of?

It's not a nagging question, just one of interest. Again, great job on the video!

Cheers!

[Boss Raptor]

Boeing, as with most manufacturers, uses many different subcontractors to make a myriad of parts and sometimes (quite usual) several different subcontractors make the same parts at the same or different times - using the same or sometimes different part nos. - some may have slight design changes/differences - I have a Boeing/Vendor part no. decode/xreference book which is the size of 3 yellow pages

[BraceBrace]

It's also done for reliability (fabrication errors in one factory). Didn't know they did this for the trim wheel, but in school they told me the 2 or 3 autopilots in an aircraft have different computer technology on the inside (or same computer technology but fabricated by different companies). Can't really confirm it myself, so perhaps someone else knows more about this.

[Boss Raptor]

Correct certainly on Airbooses - 4 out of 5 of the comps/CDU's made by SFIM or is it Sextant if I recall and one by um' someone in Germany to allow for total redundancy and the risk that a particular fault will not be replicated by both design teams! - on older acft no this is not the case as the acft are less dependant