B737 Aileron transfer mechanism

[bwheelz05]

Good evening,

This afternoon we had a discussion about the aileron transfer mechanism and what the FO cables AA and AB R/H are actually 'doing' during normal (non-impeded) movement of the the yokes...

Are the cables 'floating' (moving) a tad amount during normal roll control movement or are they actually moving the same FULL amount as the L/H AA/AB cables?

I understand at 117 LBS('ish) the transfer mechanism disengages and allows the spoiler control drum to affect FULL movement into the spoiler mechanism (FO yoke only) after 12 degrees is reached thru the R/H AA and AB cables but information is somewhat sketchy as to whether the cables are normally moving a slight amount and do not move until the 12 degree turn thru is accomplished? We haven't had much work with the transfer mechanism besides its funct test during C-Checks... no one here seems to have messes with them maintenance wise beyond that.

Would appreciate some thoughts/clarification on it. Have read the SSM and AMM. Did not find anything relevant in the CMM.

[spannerhead]

Wow it's been many years since I worked the 737 and I did specialise in flight control rigging. This is from memory......

Aileron control is always via the LH AA and AB cables. These cables rotate the aileron control quadrant in the LH wheel bay. This movement of the aileron control quadrant transmits through the spring strut and rotates the spoiler control quadrant in the RH wheel bay (may be called the RH aileron control quadrant). Movement of the spoiler control quadrant effectively backdrives the RH AA and AB cables to maintain a gap either side of the lost motion device underneath the RH control column. Turning the RH control column will (through cables ACBA and ACBB) drive the LH AA and AB cables which through the spring strut will backdrive the RH AA and AB cables maintaining that gap either side of the lost motion device. So yeah under normal operation both LH and RH AA and AB cable movement is identical but the RH cables are in effect driven by the LH AA and AB cables through the spring strut. That's my understanding.

[bwheelz05]

Excellent! Very well explained. Thank you for the clarification

[Yeelep]

Its exactly as Spannerhead described, good memory.

[spannerhead]

I now work on Airbus 330 and B777, FBW just ain't the same! Control cable rigging will pretty soon be a skill not practiced by many...enjoy it while you can gents.