Engine Surging

[BrakeSnake]

I'd like to know if anyone out there can share any information they might have on engine surges, preferably from those of you who have actually experienced a surging civil turbofan engine.
I understand the theory behind the condition of surging, i.e that the engine is demanding a pressure rise which the compressor blading cannot sustain, resulting in airflow breakdown within the compressor and thus the reversal of flow which causes the hot high pressure combustion gases to be expelled through the front of the machine. This is seen on the test rigs as a cyclic rising of pressure in front of the machine, and a expulsion/suction of visible flames (accompanied by 'banging' noises) from the front of the compressor.
The engine has now begun to operate off its working line and has moved past the surge line into the unstable area of its operating envelope. Fine. All this theory is good. What i would like to know, is what indications you would expect to see on flightdeck instrumentation, and what sort of ambient/atmospheric conditions are required (combined with flight phase and type of performance demanded from engine) to make a MODERN engine susceptible to surging. If any of you out there could reply with info on your experiences of engine surges i would be extremely grateful. If the following could be included;
1)Aircraft type
2)Engine type
3)Flight phase (i.e climb)
4)Flight condtions (atmospheric)
5)Altitude
6)Speed
7)Engine demands
8)Flight deck indications before/ during/after surge (EPR, N1 trends etc)
9)Corrective action and outcome

I know that this sounds like a lot, but I would be very grateful as I recently encountered a not very nice engine shutdown over Spain and suspect it to be due to an irrecoverable engine surge condition.

Thanks for the help chaps.

Safe flying.

[This message has been edited by BrakeSnake (edited 05 January 2001).]

[spannersatcx]

BrakeSnake, can't tell you what it's like in the air, but have experienced a few on the ground. RB211 on 747, oat +10C, wind 2knots across the nose of the a/c, (I was observing on this occasion)Engine surged at low power around 1.2 EPR, 1st indications are normally a different sound coming from the fan, hard to describe the sound a change in pitch and rumbling, most good engineers would catch the surge or impending surge at this stage, if the engine is further accelerated you would then experience a fluctuation in EPR and/or EGT, egt +- 60-100C, and ff, if you kept going to the bang egt could go off scale and the a/c would shudder. In this instance as the no1 eng was running the a/c lurched quite violently as the engine surged.
JT9's would quite often surge at TOD, and there used to be a saying that when surging the JT9 was saying hello and the RR was saying goodbye. JT9's were sorted out through improved bleed control. Hope this helps a little.

[exeng]

Had a few TOD surges on the JT9D over the years. They varied in severity but all auto-recovered. No big deal really.


Regards
Exeng

[DoctorA300]

Hi BrakeSnake,
Engine surging is not normally caused by pressure demands, normally it would be airflow disturbances witch would then, as you correctly write, cause flow stagnation in the compressor.
You would most often experience an engine surge when the engine is accelerating or deccelerating, and most often an ´Off Idle` surge ei in the intial accel. from idle. Stadystate surges (in cruise ex.) would most likely be caused by a technical problem in the airflow control system on the engine(EEC/FADEC), but I have once experienced that a High Pressure bleed valve on a JT9D-59A caused a series of really bad compressor surges.
Hopes this will help you

[Genghis the Engineer]

Not a civil type, but if it's any use to you...


1)Aircraft type

Jaguar T2a

2)Engine type

Adour


3)Flight phase (i.e climb)

Turning flight at about 2g following a ground controlled avoiding instruction.

4)Flight condtions (atmospheric)

In cloud

5)Altitude

FL300

6)Speed

Don't recall, probably around M=0.6 to 0.7

7)Engine demands

Sounded and felt like somebody was machine gunning the back of my seat. Lasted about 2-3 seconds and scared the **** out of me.

8)Flight deck indications before/ during/after surge (EPR, N1 trends etc)

I honestly don't remember about before, but seem to recall a drop in N1 and high EGT for a minute or two afterwards; I'm not very sure of that either.

9)Corrective action and outcome

Continued sortie, reported to ground staff, entered in F700 told not to worry about it.

G

[Justin Cyder-Belvoir]

Double engine surge in a 125 with Vipers.
Level flight @ FL55 VMC ias about 250kts S&L no thottle movemnt hence engines stable.

Both surged; felt like airbrake had been extended. Lots of vibration and juddering.
RPM indicator swinging from 100% to 0%, TGT low can't recall too much else. Cause was incorrectly set bleed valves.

[togaroo]

Ive been on the ground and heard a Pratt & Whitney JT9 turbo fan grumble and stall whilst doing engine runs - its not a pretty sound. Factos that can influence this is a tailwind in the exhaust pipe or large gust accross the inlet can have a dramatic effect on the possibilities of engine stall. The thing that gives it away is the surge - grumbling that you hear as the conditon develops and then bang as the stall occurs. If the engine is fitted with eng vibration monitors like the old classic 747 - a surge / stall is positively identified by the change in the eng vibes. Also the bang you can hear on the ground rather gives it away. Apart from scaring the pants off you - its not really good on the stators & rotors and if severe enough leads to blade / vane damage.
As I have described its all obvious after the fact, but can be difficult to detect or prevent. The early turbofans were very susceptible but now with FADEC control these type of events are les likely to happen and if they do occur you have less control over them apart from the obvious actions.


------------------
Its life Jim, but not as we know it!!

[BrakeSnake]

Thanks guys. Just got info back from the company about my experience and it ties in with whats been posted. We were in the cruise at FL350, moderate turbulence, non-icing conditions. The ATS demanded an engine deceleration as we had encountered a positive wind shear. As the thrust levers were brought forward again to maintain the selected speed, a low vibraion was felt/ heard. The left engine (RR Tay) had not responded and N1, N2's were stagnant (fluctuating) with an EPR of about 0.6. The TGT then went throught the roof and stayed there (about 900 C). The engine failed before we could shut it down (in all about 12 seconds from no engine responce). The engineers have told us that the Airflow Control Regulator Valve had failed, resulting in engine surge.

Thanks again chaps.