Improperly Stowed Thrust Reverser

[Poose]

Folks,

Currently debating a question in the workplace - would a thrust reverser show up as improperly stowed or unlocked as part of your Power Checks?
Would that provide sufficient force to trigger a warning?
Any insights would be appreciate!

Thanks

Poose

[matkat]

Thrust revers have position switches if the sensor is far enough away a reverser not stowed light will show up on the CWP when it is fully deployed and the sensor will activate a 'reverser operating' light on the CWP, a power check would not activate the light either way as its either in position or its not. This a basic guide.

[Poose]

Matkat,

Thanks for the quick response!

So... In essence, my question is:

"Would the force of the engines during pre-flight Power Checks be sufficient to 'displace' the reverser enough to trip the microswitches and cause the warning to show on the Central Warning Panel?"

[matkat]

I am sure there could be a case for that but have never seen it, years ago I was a flight tech on L1011s and you would occasionally see the reverser not stowed light flickering but this was more of a design issue than the reverser actually being unlocked.

[Poose]

So... the intention of the warning is to warn a crew in flight that the reverser is unlocked as opposed to warning them before departure?

I have a meeting to discuss a hypothetical question surrounding this eventuality, so any insights are most helpful! :8

[rudderrudderrat]

Hi Poose,
the intention of the warning is to warn a crew in flight that the reverser is unlocked as opposed to warning them before departure?
It's purpose is to warn crews that it is not locked in the fwd thrust position both on the ground & in flight. It could be very messy if you tried to take off with one unlocked and you didn't know about it until airborne.

It can sometimes be cleared by selecting reverse idle with the engine running, then selecting fwd idle to let the stowing logic run.

[Poose]

Thanks for the feedback, gentlemen! :ok:

So... it's not a given that an unlocked reverser would show up as part of the Power Checks?

Secondly, am I right in assuming that if an unlocked reverser warning could not be 'cleared' you would abort the flight and taxi back to the ramp?

[StephenHealey]

It can sometimes be cleared by selecting reverse idle with the engine running

[KBPsen]

Poose,

From your line of questions I am not sure you understand yourself what it is you are asking about.

What "pre-flight Power Checks"?

A thrust reverser system that is not in a secure position will cause a warning. Be it the position of the translating sleeves, the position of any locks or the position of valves that control the power to drive units.

[Shiny side down]

What aircraft?

I know of one recent incident where a reverser 'unlocked' light has resulted in an abort, even though normal starts were carried out.

On another type from many years ago, the reversers had some issues occasionally, resulting in one not stowing correctly after use. Reported later by a maintenance company after routine maintenance, that they had to do a lot of unexpected work on the reversers due to previously poor maintenance.

If the problem doesn't clear after carrying out all normal and rational efforts to do so, then returning to stand seems appropriate.

Several smaller corporate aircraft have procedures checking the reversers operation during after start. Is this such an aircraft?

[dhardesthard]

We need to know what engine and on what A/C it is fitted. What "power checks" are you referring to?

[Basil]

Poose,
A 'Power Check' is not carried out on any jet I've flown unless for a specific technical reason.

[TURIN]

Poose, a review of this may help.....

BA747 T/Rev in flight. (http://www.pprune.org/rumours-news/373713-ba056-jnb-lhr-incident.html)

[Poose]

Thanks for the replies!

I think I realise where there may be some misunderstanding...

The biggest thing I've ever flown is a light twin and I assumed that jet aircraft did a 'power check' like you would in one of those, or a single engine piston - prior to departure at the holding point...

In essence; I thought that jet aircraft at some stage went to a 'higher' power setting beyond idle or whatever you set the engines at while holding on the ground (prior to departure); as some sort of 'power check' - to check certain systems - one thing being (my concern) that the thrust reverser's were locked, before attempting to take off.

Just trying to establish whether or not an unlocked thrust reverser would always be detected on the ground prior to take-off.

My question surrounds light/business jets, primarily.

[Basil]

Nearest to that we'd do is:
start takeoff roll
check all stabilised at 1.2EPR just to check that one isn't lagging, malfunctioning etc.
set t/o thrust

[Poose]

Basil,

If, as you describe, discovered the reverser to be lagging/unlocked during the take-off run, albeit below V1, would you then reject the take-off?

[FE Hoppy]

What Aircraft are you referring to?

On some aircraft the Reverser unlocked warning is triggered by as little as one of four reverser locks not indicating locked.

This means that the reverser doesn't have to move at all to trigger the failure.


A take off would be rejected from low speed when the engine failed to accelerate. Most engines have an interlock that will force idle thrust with a TR failure so when the crew try to set TO thrust the engine would fail to accelerate and the take off would be rejected. The flying pilot would notice the asymmetry immediately so you wouldn't get close to V1.

If a Reverser unlocked during the take off roll the thrust reduction would trigger the rejected take off below V1.

[dixi188]

Poose,

Jets don't do pre take off power checks. If they did, imagine the jet blast of a 747 on the next A/C in line at the holding point. No room to turn 45 degrees.

If a reverser is unlocked then a warning will appear. (Assuming the correct maintenance procedures were applied)

If during take off or flight a reverse unlocked indication appears then the immediate action is to close the power lever of the affected engine. If below V1 then Stop.

The Lauder Air crash on 26 May 1991 was due to an un-commanded thrust reverser deployment in flight. The situation was un recoverable after less than 10 seconds.

I've had a reverse unlock indication after start and that involved shut down and maintenance action to lock out the reverser before dispatch IAW the MEL.

Hope this helps,
Dixi.

[grounded27]

It is actually quite the opposite, mechanically most "c duct" reversers would want to stow with additional power. Generally unwanted deployment is a result of a pneumatic control valve failure or control circuit. I love hydraulic reversers!

[Poose]

Gentlemen,

You've really aided an Engineer's understanding.

This has been really helpful!

Thanks for your time! :ok:

Poose

[mono]

Just to further clarify,

A reverser unlocked indication on every a/c I have worked on does not require the engines to be running (tho' many types do require engines running (or a maintenance over-ride) to operate the reversers). If electrical power is applied and a translating sleeve/deflector door is unlocked then an amber REV indication will show.

Power checks are not carried out prior to each flight (no mags to worry about & no need to get the engine oil up to temp)

[Denti]

Actually, engine oil needs to be within limits before take off, but that is usually done by the time you reach the runway, except in extremely cold climates with a cold soaked engine.

[Flightmech]

As previously stated a thrust reverser sleeve not in the fully stowed position will provide a warning even if the engine is not running. It's always good to debrief the inbound MD-11 crew only to find the dreaded amber "U/L" displayed in the middle of the #2 engine N1 indicator:{

[lomapaseo]

All kinds of reversers (just like planes) and all kinds of logic and safe guards.

However, with the lessons learned in most transport jets, an unwanted reverser deployment can be bad news. Thus the need for weight on wheels switches, reverser unlock switches and FCOM manuals of what to do.

Simply as one poster has already said if below V1 abort, if above V1 bring the engine to idle ... and leave it there. (one guy didn't and upon reapplying thrust the reverser deployed)

Most protection logic in the design should auto-command a stow of the reverser for a simple unlock light warning if there is no weight on wheels. However its still up to the pilot to command the engine to idle.