"EPR increases while N1 remains stable. Read the Swiftair MD-83 accident report for full details: https://reports.aviation-safety.net/...D83_EC-LTV.pdf"

I think Nik was referring to the P3 pressure pipe on the engine not the P2 sensor on the nose cone

PT2 IS on the engine, located in the middle of the inlet cone on the JT8-D (a small tube at the side of the inlet on many other engine models). It was mis-translated from the original French in the report. PT3 is between the LPC and the HPC if my memory is correct. Same thing happened with Air Florida...

For the CFM 56

The PS3 static pressure pick-up is located on the combustion case, at the 9 o’clock position, between two fuel nozzles.

nikplane

I can't keep up with the responses to this question so far

Sticking to this engine model can you precise the reason for your question as well as the location of the sensor you are talking about and of course what possible reason for blocking?

Lomapaseo, unless I'm mistaken Nik was alluding to the fact a blocked P3 pipe could dramatically effect the engine indications and basically that may be a factor, if indeed the engine had anything to do with this event.

On the CFM 56 the P3 pipe connects from the side of the combustion case at the 9 o'clock position, its a formed metal pipe, and gives HPC discharge pressure to the ECU, this enters BOTH channels on the ECU and then is converted to by the MEC/HMU to give movement to the valves in the fuel control unit and hence shaft speed. These P3 tubes are metal and have a drain hole at the lowest point, normally only water would collect and be drained away. ice perhaps but unlikely in normal conditions. The P3 is just one of 5 pressure sensors and does not work in isolation from other signals which are used by the ECU.
If for some unknown reason the P3 line was blocked the ECU may not be able to compute a model to adjust the fuel flow within the range from Surge to Flame out and indications would be erratic, but erratic engine indications are something we are trained for in the sim, and assuming one engine is running "normally" there is always comparison to be drawn to assist diagnosis. When unusual parameters are observed they should be entered in the comments section on the TLB to assist the engineers. One presumes the previously reported A/T malfunctions would have been investigated

Outstanding clarification (even it' not what Nik meant :))

But working with your explanation could anybody suggest why this unique minor failure mode has crept into this discussion thread?. Where is the relevancy in findings to-date?

GUYS!!!
Stop and hold. You're talking about the FADEC CFM56-7 on the NG. This was a 737-500 which has the CFM56-3!!! It's NOT FADEC! There is no FCU, P3 feeds directly into the hydromechanical control.
Lets get back to the scenario at hand.

Even by pprune standards, this is the most ridiculously specific speculation based on the scarce available factual evidence

I can feel the armchair seat restraints tightening at this comment

Er..... EPR?.... that may suit a -100/200 cuz they had JT8s.. The CFM-56-3 on the B737-500 has N1, EGT N2 etc.... no EPR. One of the nice things of using N1 for power is that it avoids an erroneous EPR indication, like Air Florida 90.

Icarus2001

Reuters:-

On Jan 19th 2021 the KNKT reported that the FDR contained 330 parameters of a total of 18 flights. The KNKT have already developed a general picture of the accident, however, need further data from the cockpit voice recorder before publishing any information. Inspections of Boeing 737-300, 737-400 and 737-500 in Indonesia have been ordered.

On Jan 22nd 2021 the KNKT confirmed a preliminary report will be released within 30 days after the accident (until Feb 8th 2021), no other information has yet been released.

On Jan 23rd 2021 the KNKT chairman stated, that the tech log of the aircraft contained an entry about an autothrottle fault a few days before the crash. There has been no other technical anomaly noted. At this time it is entirely unclear whether or not problems with the autothrottle contributed to the crash Crews can easily fly the aircraft manually without the autothrottle system. The CVR will be needed to hear the discussions between the pilots to identify the actual problem they had at hand. (Editorial note: obviously this entire statement came in response to speculations raised by a number of media globally attributing the crash to a malfunction of the autothrottle system).

On Feb 2nd 2021 the KNKT chairman said in a press conference, that reports distributed by western media about a possible autothrottle malfunction causing asymmetric thrust are wrong. However, the KNKT sent 5 pieces of debris, including the autothrottle unit (but not identifying the other parts), to the USA and UK for further examination stating they want to find out why an autothrottle parameter changed. He re-iterated they don't know why that parameter changed and need confirmation from the parts sent to the USA and UK and the CVR. The maritime search for the CVR is still ongoing.

zero/zero

I think you are right. Why do we need to discuss things like "its a formed metal pipe, and gives HPC discharge pressure to the ECU,......." when the internal workings of a jet engine have nothing to do with the conversation and in any event there is an excellent Engineering Forum on PPrune for those who love the granular construction of turbine blades etc. My point actually is that an engine failure or an auto throttle failure are non events to a trained pilot. So either it was something else, or we have a case of something going wrong with something like pilot training. Not the pilots you see. No pilot sets out to do anything but his or her best. Retired Guy

It's quite normal to answer a question when asked, doesn't mean we are agreeing with the rumoured causes of the event.. on the other hand stating the obvious Can we agree, as the aircraft crashed it was in fact, "something else"!

fdr

It's ok to talk about EPR if you describe what is going on inside an engine. However if you're talking about what a pilots sees then you need to keep to the actual engine cockpit displays. For myself I like to keep to what a pilots sees and only divert to the actual engine operation-cycle to figure out why.

let's move on since I lost track of where we got to in the last week :)

OK, so how about this:
Can anyone say why the Indonesian KNKT has sent bits of the plane to the UK?
The French have more parts onboard a 737 (half an engine at least).
Could it be the UK is still respected. Joy in these Brexit times.

Having fewer national parts on board would presumably be seen as a good thing if an independent perspective was being sought. French involvement in the engines, versus the potential for asymmetric thrust to be a factor? Seems to me a more likely basis for such a decision than respect for any particular state.

Didn’t Smiths Industries make the auto-throttle computers for the classic. If the auto throttle system is being looked at would those be the parts being sent to the U.K. ? That’s total speculation, btw.

Interesting snippet of information released by AVH today. Last communication with aircraft was request for heading 075 to deviate around weather, which was granted. Crew acknowledged clearance. Subsequently a/c was observed turning left on radar instead of right to 075, did not respond to ATC query.

General Electric bought Smiths years ago and renamed them GE Aviation Systems. They're currently headquartered in Cincinnati OH. Not familiar with where the auto-throttle folks ended up, but one former Smiths division that I know of has been resold once and relocated twice since the GE acquisition, and is currently located in Ft Collins, Colorado. They had initially started as part of Dowty-Rotol.

Parts being sent to US
 

https://www.thejakartapost.com/news/...or-checks.html

some possibility that parts like the engine FCU may be examined for mechanical and operation issues (sticky valves ?)

Some times there are issues about the fuel itself and the best place to get a sample is from the undamaged innards of the FCU on an engine. Any issues involving the FCU include before disassembly x-rays of where the valves are set.

I guess we'll just have to wait for an interim report before second guessing why they are sending parts to the US