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I was wondering what kind of low pressure indication causes abnormal variations in the RPM of a Lockheed L188 Electra. I was told one of the engines was presenting low pressure readings at certain rotations. Would that be low engine oil pressure? I have read the Electra manual and only saw indication of low pressure for either hydraulics or engine oil. The call of low pressure was originally made by the FE, which makes me think it should be something that would show somewhere in the flight station. Thanks

In this link the only relevant low pressure indications I found were of engine oil and of hydraulics. https://publicapps.caa.co.uk/docs/33/SRG_ACP_L188_REV2_ALL.PDF . Presumably everything should be there, although I was subsequently told that it could also refer to manifold pressure.

Here, https://www.spruemaster.com/blog/wp-content/gallery/manual/Lockheed%20L-188%20Electra%20-%20%20Electra%20Flight%20Control%20S%20ystem%20Part%201.pdf , on page 30, fig.24, there is a picture of the flight station . I had originally only seen the four lights indicating low engine oil pressure (top left corner, listed as part of the "Ess Ac Inst Bus"), but upon closer examination, I found other things related to pressure as well. Perhaps I was biased because the first documents I read only mentioned hydraulics and engine oil.

So I guess my question should be: what kind of low pressure is the cause of (or is caused by - the Captain was not very clear) abnormal RPM readings. Thanks a lot

Ps: I tried to upload the flight station image here, but didn't manage. It sad it was too big. My apologies.

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    $\begingroup$ Could you clarify your question? 1/ "low pressure indication causes abnormal variations in the RPM" and 2/"one of the engines was presenting low pressure readings at certain rotations". In one case low pressure is the cause of RPM variation, in the other case specific RPM are the cause of low pressure. What is the actual chain of events you want to be explained? $\endgroup$ – mins Aug 20 '17 at 14:46
  • $\begingroup$ What do you mean by "kind of low pressure"? You may specify if you what to discriminate fuild circuit (hydraulic, oil, fuel,...) or the causes of this low pressure inside on kind of fluid circuit. $\endgroup$ – Manu H Aug 25 '17 at 19:00
  • $\begingroup$ Leave open but we will need a little more clarification from the OP before this can be accurately addressed. $\endgroup$ – Carlo Felicione Aug 25 '17 at 22:00
  • $\begingroup$ @ mins - thank you for pointing that out. I actually only transcribed what the Captain had said , so it never crossed my mind to evaluate whether they made sense. But you are right, they did sound contradictory. As it was the FE that called the low pressure first , I think DeltaLima edited it correctly, leaving the first part of the question in and removing the second. Thanks $\endgroup$ – Electra Aug 26 '17 at 18:02
  • $\begingroup$ @ Manu H - I added some more information to the question. I do not know what kind of low pressure we are talking about, which is why I came here for help. I realise than when talking about an aircraft there are loads of options and I did try my best to find out to which of those the Captain was referring to, but I have failed nonetheless. At this point I am almost sure that we are referring to low engine oil pressure, but I needed to be sure if that would cause abnormal RPM readings (or be caused by). Thanks $\endgroup$ – Electra Aug 26 '17 at 18:42

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