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N1 - 0, N2 - 0 (737 argument with an instructor)

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N1 - 0, N2 - 0 (737 argument with an instructor)

Old 17th Nov 2020, 15:28
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N1 - 0, N2 - 0 (737 argument with an instructor)

Hello, dear colleagues

Some month ago I had flew with a simulator session on B737CL as a first officer.
Everything went well and at some point I had an Engine Malfunction after V1. Seemed like an engine failure, I reacted very well and kept the aircraft on runway heading. Approaching to 800ft AGL I was told by the first officer that we have an engine failure. But, before making a decision on the actions I need to take, I studied the engine indications. So that is what I am sure of: N1 indicated 0, N2 indicated 0. I have been trained that this indicated an Engine Severe Damage, which made me call for a memory drill of the appropriate checklist.



But after that, I was interrupted by the instructor Ė stating that he gave me a simple engine failure. My argument about N1 and N2 indications being at point ZERO did not suit him, as it is not stated in any Boeing 737 Manual.

We did not find any agreement at that point. Please guys, any advices on the topic Ė except for the basic knowledge and some obvious facts.



Best regards!
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Old 17th Nov 2020, 17:55
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These are the conditions from the 737 QRH for Severe Damage.

Condition: One or more of these occur:
•Engine fire warning
•Airframe vibrations with abnormal engine indications
•Engine separation.

You had abnormal engine indications but if this was not accompanied by airframe vibrations then it doesn’t meet the condition for Severe Damage. Practically I think this is only possible in a simulator. In the aircraft, the chances of both spools stopped with no airframe vibration is virtually impossible. A signal failure to both indicators may do this but then you may not lose thrust. So, in my opinion, your instructor is technically correct but it’s not a likely scenario for real. Sounds like that sim puts N1 and N2 to zero when Engine Flameout is selected.
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Old 17th Nov 2020, 18:33
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If you are at flying speed, the N1 must have some rotation unless it is seized (on the ramp the fan turns in the wind). Different airframe, but still jet technology, Airbus would suggest treating no rotation as damage.
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Old 17th Nov 2020, 18:41
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Originally Posted by Capt Scribble View Post
If you are at flying speed, the N1 must have some rotation unless it is seized (on the ramp the fan turns in the wind). Different airframe, but still jet technology, Airbus would suggest treating no rotation as damage.
I tend to agree with this. Itíd at least be windmilling. The simulator is just that- a simulator. Itís not perfect. Sometimes you just have to nod and smile.
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Old 17th Nov 2020, 19:12
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Capt. and Check have said, it'd be pretty much impossible to have zero rotational speed on both rotors without severe engine damage. It could be an indication problem, but there are multiple independent data paths involved for rotor speed that would all have to be failed for that to happen - again, very, very unlikely without severe engine damage (or even separation).
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Old 17th Nov 2020, 19:27
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Yes a loss of engine rpm to zero is either loss of signal or locked rotors. Locked rotors are extremely rare. in-flight (too much wind and the broken pieces loosen up) Both rotors being locked in flight is way outside the data base experience but I uppose it could happen

Airframe vibration associated with loss of thrust and any other any engine symptom is time to wake up and follow the FCOM,

The simulators you are typically trained on cannot reliably replicate these combination so a typical training syllabus often simulates something akin to multiple engine symptoms to the point of training you to go deeper into decision making.

Real life events that progress in the powerplant beyond the first seconds following a severe engine failure are indeed rare
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Old 17th Nov 2020, 20:16
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IT seems that your simulator is slightly unrealistic and your instructor is not making due allowance for this.
If all rotation came to a sudden stop, some vibration (probably a lot of vibration) would precede it.
Once completely seized, the vibration could then cease.
Further, as it seized there would probably be a spike in EGT.
It is better when in doubt to run the worst case checklist. That is the Severe Damage checklist. The engine is buggered anyway, so what more harm could you do?
Also consider that fire detection and EGT systems are not infallible. You could have a fire or severe over temp which is not obvious. When in doubt do the full drill.
Straight flameouts at takeoff are less likely, and would suggest either a fuel problem (at this stage this would probably be unknown) or environmental (which would be fairly obvious). Healthy engines don’t suddenly stop with no residual rotation.
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Old 17th Nov 2020, 20:30
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Had it happen to me...

Years ago, during take off right about at V1, had the left engine N2 seize. Thought the left wing was coming off. Whole airplane shook like crazy. First flight of the day; early morning departure. Woke us up for sure.

This was only for a few seconds. Once the N2 was completely stopped, all the violence stopped.

Our SOP at the time was to execute the ďEngine Fire, Severe Damage, SeparationĒ checklist. Since we never got an actual fire indication, we stopped the checklist just shy of discharging a fire bottle.

Canít remember what actual N1 and N2 RPMs are at take off thrust, but itís a lot. (Maybe 14,500 RPM....dunno?)
For such mass to come to a complete stop in a matter of seconds, itís a violent experience. I know this; it actually happened to me.

Fly safe,

PantLoad
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Old 17th Nov 2020, 20:47
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Iíd treat zero N1 and zero N2 as severe damage if there is an associated swing (otherwise itís a failed indication in my book). And doing the severe damage separation memory items is not unsafe if an engine is failing/ has failed. I am not a TRE or a TRI or a trainer in any respect but I personally think the instructor was wrong to stop the simulator at that point. Have a discussion in the debrief by all means but not during the exercise.
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Old 17th Nov 2020, 21:02
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Were you one of two first officers, or in command? Or am I pointing out the obvious?
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Old 17th Nov 2020, 22:15
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Airbus says that the following list allows to suspect engine damage :
Rapid increase of EGT above the red line
Important mismatch of the rotor speeds, or no rotation
Significant increase of aircraft vibrations, or buffeting, or both
Hydraulic system loss
Repeated or not controllable engine stalls

The manual states that two or more are required, but in every sim i ever did in an airbus (two different countries, a dozen of instructors from 6 different airlines), no rotation on either N1 or N2 was engine damage.
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Old 17th Nov 2020, 22:25
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10 years in CL and we were taught no rotation = severe damage.
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Old 17th Nov 2020, 22:42
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Originally Posted by Beakor View Post
These are the conditions from the 737 QRH for Severe Damage.

Condition: One or more of these occur:
ēEngine fire warning
ēAirframe vibrations with abnormal engine indications
ēEngine separation.

You had abnormal engine indications but if this was not accompanied by airframe vibrations then it doesnít meet the condition for Severe Damage. Practically I think this is only possible in a simulator. In the aircraft, the chances of both spools stopped with no airframe vibration is virtually impossible. A signal failure to both indicators may do this but then you may not lose thrust. So, in my opinion, your instructor is technically correct but itís not a likely scenario for real. Sounds like that sim puts N1 and N2 to zero when Engine Flameout is selected.
To the letter of the law, this ^^^

Itís quite rightly been pointed out that the likelihood of having no airframe vibration if you have both rotors locked is probably nil.

However, you do exactly what it says on the tin (i.e. donít do severe damage without airframe vibration) and youíll have something to stand by in court. The correct checklist would obviously be Surge/Limit/Stall which will lead you into a shutdown for this condition anyway. In a real incident, a sneaky lawyer might find some reason to ping the blame on you for a subsequent problem by showing you donít know the manuals for your engine situation. Anything done outside them must able to be justified in court. Sucks, because I think we all know that two locked rotors must be severe damage. I think in the sim I would let this play and raise it as a talking point. If it was handled safely then the box has been ticked for engine-out handling.
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Old 17th Nov 2020, 23:01
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Are we talking a full motion simulator? If it's a fixed simulator, it would be pretty hard to simulate airframe vibration...
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Old 17th Nov 2020, 23:06
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What was his point? I don't know the 737, but the only difference is pulling/pushing the fire handle on any Boeing or Airbus I've flown. In the highly unlikely event that you need to restart the thing, it's reversible anyway.

A sim is a good procedure trainer but any instructor or examiner needs to point out that a lot of it is "best guess" anyway. Next time you get a sim TCAS RA, watch what the intruder does. It follows you. Would that happen in the real world?
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Old 18th Nov 2020, 00:26
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I am currently working as a 737 Sim Instructor. We teach no rotation equals severe damage. On the instructors panel, selecting this function simulates no N1 and no N2 with no vibration. The only difference to a straight failure being a distinct 'pop' during the actual failure itself. If the candidates treat it as a simple failure to be tackled at the end of the fourth segment, it programs a fire before they reach this point. The Civil Aviation authority we work under treat no rotation as severe damage and expect shutdown in the second segment.

I have had a failure of this nature in real life, although it was a JT8D. It sounded like a bucket of bolts spinning around with initial vibration but once it seized, no vibration at all. There are limitations to even modern simulators and despite the, 'Just like the real thing' sing song they are not and never will be.

Last edited by By George; 18th Nov 2020 at 00:41.
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Old 18th Nov 2020, 00:38
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Possible cause:

The instructor actioned a simple failure on his controls - and thus were right, while at the same time
The student saw N1 = 0 and evaluated severe damage - which is what needs to be done on the real aircraft.

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Old 18th Nov 2020, 04:21
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Originally Posted by By George View Post
I am currently working as a 737 Sim Instructor. We teach no rotation equals severe damage. On the instructors panel, selecting this function simulates no N1 and no N2 with no vibration. The only difference to a straight failure being a distinct 'pop' during the actual failure itself. If the candidates treat it as a simple failure to be tackled at the end of the fourth segment, it programs a fire before they reach this point. The Civil Aviation authority we work under treat no rotation as severe damage and expect shutdown in the second segment.

I have had a failure of this nature in real life, although it was a JT8D. It sounded like a bucket of bolts spinning around with initial vibration but once it seized, no vibration at all. There are limitations to even modern simulators and despite the, 'Just like the real thing' sing song they are not and never will be.
I’m posting from a decaying memory here (and I know someone will correct me if wrong!) but I recall that there is a difference with approach/attitude from the airframe manufacturers (and hence data providers and these days often the source of the software model) with issues such as “Severe Engine Malfunctions” and “Engine response to Volcanic Ash encounters”.

Whilst Airbus and others suppliers support these types of malfunctions with vibrations, sometimes quite severe or erratic engine indications and or shutdowns being experienced, Boeing tends to take a different approach and has stated that there is no or insufficient data for them to provide the model.

The TDMs of course are obligated to only meet approved data.
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Old 18th Nov 2020, 05:15
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In fact what I wrote is a bit confusing. We were 2 first officers training in one session.
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Old 18th Nov 2020, 06:54
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In the simulator I operate (B737-300 Category D Full Flight), a flame out initiated on the instructor panel gives instant loss of thrust and a yaw and roll in the direction of the "dead" engine. The N1 and N2 decay until eventually the N2 and N1 show low numbers but continue to rotate slowly under influence of forward speed. There is no vibration. The follow up checklists do not require the crew to pull the fire handles.
There is an item on the instructor panel annotated "Engine Seizure." When actuated, there is instant loud engine noise associated with the engine running down and seizing. At the same time there is the expected yaw and roll towards the seized engine. There is severe vibration which is absolutly unmistakeable physically as well showing up on the relevant vibration indicator. .

In this simulator the N1 will quickly fall to zero caused by the failure of the drive shaft from the accessories gear box, while the N2 will run down more slowly. It is the zero reading on the N1 that is a characteristic of a seized rotor. That, and the severe vibration on that engine that would trigger the Severe Damage checklist rather than a mere engine flameout checklist.

Be careful here if the vibration indicators are EFIS type and not analogue. The needle on the EFIS dial is very small. Beyond a certain vibration limit that needle vanishes off screen. I believe that was one of the problems associated with the Boeing 737-400 crash at East Midlands where mis-identification of the failed engine occurred. In this event the EFIS vibration indicator needle disappeared off screen because it had registered a high reading beyond the capability of the vibration system and thus showed no reading at all on the gauge. It is wise therefore to look for corroborative evidence of severe damage or otherwise rather than rely solely on one source of information

See: https://en.wikipedia.org/wiki/Kegworth_air_disaster

One extract from that report stated:"The vibration indicators were smaller than on the previous versions of the 737 in which the pilots had the majority of their experience. The dials on the two vibration gauges (one for each engine) were small and the LED needle went around the outside of the dial as opposed to the inside of the dial as in the previous 737 series aircraft. The pilots had received no simulator training on the new model, as no simulator for the 737-400 existed in the UK at that time. At the time, vibration indicators were known for being unreliable[3]:69–70 (and normally ignored by pilots), but unknown to the pilots, this was one of the first aircraft to have a very accurate vibration readout."

Post No 2 says it all. If your simulator has the N1 and N2 gauges falling to zero readings simultaneously when on the instructor panel the instructor has selected a simple flameout engine failure, this would suggest the simulator fidelity fails to meet that of a Level D category full flight simulator. Your instructor should be aware of this. If your simulator is a no motion operation then there will be no vibration present. This should have been briefed by the instructor concerned.

Be aware that pedantic simulator instructors exist and you could court retribution if you attempt to argue with these type of characters. A fact of life in simulator training. The QRH/FCOM are your friends when it comes to differences of technical opinion.
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