Question - Circumstances when systems are 'locked-out'?

[Simon150]

Hi,

I was looking for a but oif insight into under what circumstances (generally) systems can be locked-out.

I have some limited experience with TRU's and I understand that with a typical system, the ICU (Isolation Control Unit) can be locked out to prevent hydraulic actuation along with a mechanical lockout on the TRU itself.

What sort of scenarios would require the TRU to be locked out, and where is the line drawn between locking-out and accepting a delay and repairing/replacing the system?

The reason I ask is that I am working on the design of an engine sub-system which is required to be non-despatch critical, but it is difficult to know where to draw the line where there is a level of failure under which the lock-out feature should be abandoned and it should be accepted that a delay whilst the system is repaired is the only option.

Are TRUs the only example of 'lock-out' features on aircraft or is there any other systems (especially non-despatch critical) that I could look at for guidance?

Hopefully you appreciate I can't be very specific on the application at this stage, but if anybody would like more detail, please ask.

Thanks in advance

Simon

[Mr @ Spotty M]

A number of components can be locked out, Thrust Reverser's, bleed valves and anti-ice valves are the most common l would think.

[Mike_s]

As said there are many things that can be locked out? Most common thing I have seen would be thrust reversers. Reasons can vary from EICAS fault messages to failure to deploy.

[spannersatcx]

Have a look at an MEL (http://fsims.faa.gov/PICResults.aspx?mode=Publication&doctype=MMEL) you will see that a lot of entries will have number installed X number required Y.

Some will have procedures on how to lock out or isolate the system/component, and what affect it may have.

[rmm]

What sort of scenarios would require the TRU to be locked out, and where is the line drawn between locking-out and accepting a delay and repairing/replacing the system?


The most common scenario would be no deployment of 1 reverser. The reasons for the fault maybe many and varied, but for example if it was traced to an actuator that say takes 3 hours to change it would be locked out and the MEL applied. The actuator would then be changed on an overnight hangar visit.

Where I work items are generally locked out/disabled to keep on time departures where possible. There are exceptions to this as well. For example an anti-ice valve maybe lock closed but the aircraft cannot fly within 5nm of rain. If this is not possible then the valve would have to be changed and the delay excepted.

Another example is a long haul flight with the IFE u/s. We will fix that and wear the delay. The pax would generally be happier with a 1 hour delay than no IFE for 12 hours. The line in the sand on this one would usually be made by an operations manager. There are crew hour limitations and schedules to take into account. So if the repairs might take 3 hours they might send the aircraft without IFE and offer the pax some kind of compensation. e.g a credit towards another flight.

[spannersatcx]

I always thought a TRU was a Transformer Rectifier Unit, and there is no way of locking these out!:ok:

[MATMAX]

spanners,
i was thinking like you and so the question from Simon was not clear to me too ...
maybe it depends if you are B1 , B2 or B1B2 ...
for me : thrust reverser : T/R
transformer : TRU
ah ! acronyms ...
FCU : fuel control unit , flight control unit , flush control unit ???
anyway , basically if a part of a system is not critical then it can be de-activated , thats the reason why the MEL exists ... and also as others said , to avoid a delay ... sometimes it is even quicker to fix the problem by a simple test than to fill the techlog...
Guys , i do not have to remember you that MELs are customized ... except under the use of the MMEL.
a simple msg can "generate" a maintenance procedure without real problem ...
Simon , may i suggest you to be more accurate ?
Rgds.

[Simon150]

No need to be more accurate, I gather most people knew what I was banging on about and the responses have been very useful. Thanks guys.

re. Acronyms, I thought the clue was in the question but hey...what do I know....what is a Transformer Rectifier Unit anyway ;-)

[dixi188]

Acronyms in aviation are a nightmare.

I've been in this game for 41 years and am amazed at the number that come up that I don't know or get confused by.

A few years ago, just for fun, we tried to do a flight without using acronyms.

So the VOR is "VHF Omni Range". Damn! "Very High Frequency Omni Range".

With acronyms whithin acronyms it soon became impossible.

The point is, when posting on here, don't assume that everybody understands your acronym.

Something in brackets as Simon 150 did with ICU can be a great help.

As for a Transformer Rectifier Unit:- It converts AC (Alternating current) into DC(Direct current) and normally reduces the Voltage from 115 to 28.

An Inverter will do the same thing in reverse.

Hope this helps.

[Busted Sump]

An A330 is basically 4000 acronyms flying in close formation.