A320: Oil pressure indication and Advisory on the ENGINE SD Page

[nelbhoy]

Hi Gents (and Ladies), at the risk of sounding stupid (which isn't hard) I have a question with regard to "Oil pressure indication and Advisory on the ENGINE SD Page". In the MEL it states that the Associated Thrust Reverser must be checked operative. Why? There is no physical tie in with engine oil and the T/R. Does the T/R need a discrete positive oil pressure signal to operate? Thanks for your time.

[flame_bringer]

Oil pressure indication is there for indication only, Discrete signals are processed from the low oil pressure switch.
Thrust reverser operates when aircraft is on ground (inhibition relay energized) and radio altitude is bellow a certain value (static relay energizes for T/R hydraulic shut off valve to open).
There is no link as far as I know however this MEL requirment is possibely there due to operational and safety reasons.
Lets see if someone else can enlighten us with a better answer.
By the way I assumed you were talking about cfm 56 engine, This does not apply to v2500.

[nelbhoy]

Thanks for your reply flame bringer. Yes it is the CFM. I understand that you will not get a discrete from an indicator, but you could get a discrete from the indicator's source, thus proving the source as serviceable. And yes, I'm sure that the MEL item is due to operational and safety reasons. Thanks again for your reply.

[nelbhoy]

another thought is......to prevent inadvertent deployment of associated T/R during landing with an engine shutdown...?

[flame_bringer]

Nelboy
If the engine had been shut t/r cannot inadvertently deploy due to the fact that your ECU would be off so the HCU won't get any command even if the levers had been put on the reverse thrust detents, plus the inhibition relay would be de-energized.
The only means to prevent inadvertent deployment is what I pointed out earlier in my previous post, A/C on gnd and radio altitude below a certain level+reverse thrust command from the micro switchs, potentiometers and resolver synchros in the throttle control unit.
This together with an engine running signal from the EIU through the low oil pressure switch+throttle control unit micro switchs command to energize the inhibition relay, And potentiometers signal to the 3 SECs with a radio altitude input to energize the Hydraulic shut off valve for the HCU to operate.
I don't think that oil quantity indication input is required for the operation of the T/R.

[flame_bringer]

In the MEL it stated that it must be checked operative as a condition to raise the MDD, It did not ask you to de-activate it which further proves that oil quantity indication is not required for it to work.

[Swedish Steve]

I understand that you will not get a discrete from an indicator,
Maybe not on an A320 but it does happen.
B737-200 Flap indicator provides the signal for flap assymetry.
B757 N3 indicator provides a signal for the speed switch.

[nani62002]

in service experience shows that some rejected takeoffs and in-flight shutdowns have been commanded because of a low oil level. how ever , a low oil level alone is not a symptom of an eng malfunction.

the low oil pr is the sign of an imminent engine failure. therefore, the published procedure must be applied.

[TinyTim2]

As with all Airbusses you need to VERY careful of hidden data/software decisions made by various boxes , NOT in the relevant AMM OR TSM . I have fallen foul of these hidden links before on Airbus and other digital aircraft . The manufacturer will tell you that they cannot possibly list every data/software action as there are too many !!!!