Sticking/Jamming B737 thrust lever(s) - Why???

[Haul By Cable]

Every so often I find myself on a 737-300 or 500 that has one or more dodgy 'sticking' thrust levers.

The symptom is invariably intermittent and no amount of FMC bite testing is going to identify the problem.

Imagine an intermediate level-off in the descent/approach, the A/T tries to advance the thrust levers and one either remains closed or advances an inch or two then jams solid (same goes for retarding on the glidepath).

We're not talking a lazy autothrottle here, I mean a hefty pressure exerted causing a sudden release and then subsequent cycling of the lever catching on a 'notch' in both directions.

These events are never fully explained due to "Ground tested satis. report further" ( familiar to all!).

Any ideas?

Many thanks, Haul.

[Olendirk]

hmm, never got such situations and im flying b737 which are 25years old

[IFixPlanes]

Check the pressure seals of the engine control cables.

[gibbo568]

As a techie, had a similar problem years ago on an F4K, not throttles, but pitch controls. Turned out to be water ingress into control cable pulley bearings, which froze at altitude, but cleared at lower levels, and was therefore hard for us guys on the ground to solve.

Eventually traced with selective use of CO2 extinguisher to cool bearings in turn!

[The Real Slim Shady]

If the system is similar to the NG it may be a sticking clutch pack.

[IFixPlanes]

Not similar.
NG = Engine control is digital
CL = Engine control by steel cable

[kijangnim]

Greetings
We had similar problems on B767 non fadec engines, and indeed it is a pain ... it looks like the cable was blocked at some stage between the thrust lever and the engines, we looked into it with the Chief pilot and discovered that non fadec engines requires extra maintenance and inspections, and lubrication for the cables.



:)

[Haul By Cable]

Thank you everyone for taking the time to reply, it's very helpful!

Cheers, Haul.

[kijangnim]

Greetings

B767 was available without cables (FBW) or with in 1990s.
:}

[Selhurst Boy]

Like Gibbo I have experienced very similar problems, due to water ingestion, freezing at altitude on B737-300. Difficult to diagnose on ground unless freezing temperatures present. Fault was confirmed diagnosed and rectified after the a/c overnighted in temperatures well below zero.