"high side runaway" - other local terms?
This is not really about "High side failure", but regarding "diagnostic a failure" I just want to share this incident that happend to one of our aircrafts a few years ago.
Nightime (midnight), VFR conditions, two-pilot crew, HEMS flight.
MGB chip light about 3 min before destination (hospital heliport), emergency checklist consulted, and decided to land at heliport. Engineer called in to check aircraft. Verified some chips on MGB plug. Changed oil, cleaned filter and hover tested it for 45 min, before new MGB chip light came on. One small chip. Same procedure again with oil and filter, and decision was taken to relocate aircraft without medical crew to nearby airfield (aprx 2 min away) and continue investigation there in the morning.
Now it was about 4:00 AM, still pitch dark, tired crew, "just" going to make a 2 min flight and then off to bed, you get the scenario.
"Known" MGB problem!
During TO, just after CDP(wherelse) a loud bang followed by a large Tq split. #1 N1 and T5 skyhigh, #2 Tq maxed on tq gage.........and all the time the pilots had that known MGB problem in their mind.
They flew out of the situation, and after Vtoss they started to take action on the situation. Confirming that it was #2 engine that was "driving the rotor" and also responding on collective change.
They carefully retarded #1 engine to idle, left it on idle, and made a running landing at the airport.
They estimated that #1 engine was at max "values" for 30-45 seconds before being retarded.
Many things could be said about this event, but it was some good airmanship that saved this flight.
I think that "ignoring" the instrument readings, and first fly out of the situation coupled with a careful analys (slow?) of the situation, prevented the crew from doing a bad (quick) decision.
The failure, a rag sucked into the #1 engine compressor
Nightime (midnight), VFR conditions, two-pilot crew, HEMS flight.
MGB chip light about 3 min before destination (hospital heliport), emergency checklist consulted, and decided to land at heliport. Engineer called in to check aircraft. Verified some chips on MGB plug. Changed oil, cleaned filter and hover tested it for 45 min, before new MGB chip light came on. One small chip. Same procedure again with oil and filter, and decision was taken to relocate aircraft without medical crew to nearby airfield (aprx 2 min away) and continue investigation there in the morning.
Now it was about 4:00 AM, still pitch dark, tired crew, "just" going to make a 2 min flight and then off to bed, you get the scenario.
"Known" MGB problem!
During TO, just after CDP(wherelse) a loud bang followed by a large Tq split. #1 N1 and T5 skyhigh, #2 Tq maxed on tq gage.........and all the time the pilots had that known MGB problem in their mind.
They flew out of the situation, and after Vtoss they started to take action on the situation. Confirming that it was #2 engine that was "driving the rotor" and also responding on collective change.
They carefully retarded #1 engine to idle, left it on idle, and made a running landing at the airport.
They estimated that #1 engine was at max "values" for 30-45 seconds before being retarded.
Many things could be said about this event, but it was some good airmanship that saved this flight.
I think that "ignoring" the instrument readings, and first fly out of the situation coupled with a careful analys (slow?) of the situation, prevented the crew from doing a bad (quick) decision.
The failure, a rag sucked into the #1 engine compressor
Helmet fire has a point...
Everyone's talking about sorting the immediate problem out which we all seem to agree on.....BUT as helmet stated; what then? You need to look objectively at what the instruments are telling you.
In the case with engine ingestion coming out of the LZ, you've now contained Nr. Which engine is to blame for the droopy (previous) Nr and low Tq settings...or is it high Tq settings on the other engine which is to blame??
It's 90% easy peezy...but that other 10% might spoil your day BIG TIME
Everyone's talking about sorting the immediate problem out which we all seem to agree on.....BUT as helmet stated; what then? You need to look objectively at what the instruments are telling you.
In the case with engine ingestion coming out of the LZ, you've now contained Nr. Which engine is to blame for the droopy (previous) Nr and low Tq settings...or is it high Tq settings on the other engine which is to blame??
It's 90% easy peezy...but that other 10% might spoil your day BIG TIME
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offshoreigor,
You are correct, on the 76 family where the operating rpm is at max, any extra power will lead to an up tick above the max beep. In some defense of my assertion otherwise, we are talking here in generic helicopter terms, so that is not a reliable cue for many helos that have some margin between normal operating rpm and max beep.
Thomas coupling,
The idea here is that added power will result in a torque split and a rise in rpm, while a power loss will result in a torque split and a droop in rpm. So, if rotor his higher, it is probably a high side faailure, if rotor is lower, it is probably a power failure on the low engine.
You are absolutely right, you must do a study of the gages, but when you do, look to the rpm first. If the rotor is up, power is up, blame the high torque engine. If the rotor is down, power is down, blame the low torque engine.
Then, use collective to keep the rotor in the green, and stabilize altutude with speed. Do not leap to slam engine levers anywhere, this is the important point. Doing nothing is better by far than doing anything bad, and there is no great rush.
Once you have a suspect, give him a fair trial before you hang him. Tell each other why it is a good idea. "The torque split and the high Nr makes me think number 1 has a high side failure, do you agree?" Actually think about what you are seeing, guys.
Take the proper engine lever in hand, confirm it, both of you, please! Then start it back gently, moving it back while spotting rotor rpm (and while not moving the collective, which will confuse you!). If the torque begins to drop, and the rotor rpm goes back to normal, you have it! Pull the bad engine about 10% below the good one, and fly home cordinating lever and collective to keep it that way.
For the interesting case where the engine was stuck at part power due to injestion (I have had this about 3 times due to internal engine problems or fuel control stickyness) the above works well. As the torque splits, the rpm will drop somewhat, so follow the rules.
One real issue in a low power situation is - Do you leave the bad engine running and fly home? If it is vastly unhealthy inside (split internal passeges that are leaking power) it could be very bad to let it run. If it is a simple sticky fuel control, no harm. But how do you know? My suggestion is to gain good oei flight, and decide the risk balance. If I am over golf courses, shut the bad guy down and go home. If over 100 miles of icy sea, leave the low one low and milk it home.
You are correct, on the 76 family where the operating rpm is at max, any extra power will lead to an up tick above the max beep. In some defense of my assertion otherwise, we are talking here in generic helicopter terms, so that is not a reliable cue for many helos that have some margin between normal operating rpm and max beep.
Thomas coupling,
The idea here is that added power will result in a torque split and a rise in rpm, while a power loss will result in a torque split and a droop in rpm. So, if rotor his higher, it is probably a high side faailure, if rotor is lower, it is probably a power failure on the low engine.
You are absolutely right, you must do a study of the gages, but when you do, look to the rpm first. If the rotor is up, power is up, blame the high torque engine. If the rotor is down, power is down, blame the low torque engine.
Then, use collective to keep the rotor in the green, and stabilize altutude with speed. Do not leap to slam engine levers anywhere, this is the important point. Doing nothing is better by far than doing anything bad, and there is no great rush.
Once you have a suspect, give him a fair trial before you hang him. Tell each other why it is a good idea. "The torque split and the high Nr makes me think number 1 has a high side failure, do you agree?" Actually think about what you are seeing, guys.
Take the proper engine lever in hand, confirm it, both of you, please! Then start it back gently, moving it back while spotting rotor rpm (and while not moving the collective, which will confuse you!). If the torque begins to drop, and the rotor rpm goes back to normal, you have it! Pull the bad engine about 10% below the good one, and fly home cordinating lever and collective to keep it that way.
For the interesting case where the engine was stuck at part power due to injestion (I have had this about 3 times due to internal engine problems or fuel control stickyness) the above works well. As the torque splits, the rpm will drop somewhat, so follow the rules.
One real issue in a low power situation is - Do you leave the bad engine running and fly home? If it is vastly unhealthy inside (split internal passeges that are leaking power) it could be very bad to let it run. If it is a simple sticky fuel control, no harm. But how do you know? My suggestion is to gain good oei flight, and decide the risk balance. If I am over golf courses, shut the bad guy down and go home. If over 100 miles of icy sea, leave the low one low and milk it home.
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A couple of years back, we had in the persian Gulf , a high side of sorts. It was refered to as Auto acceleration, caused by fuel leaking into the bearing on the N1 govenor shaft in the FCU side on a bell 412 EP. This had the effect of drying the bearing causing it to seize and the shaft broke. The result was very instant rise of N2 / NR and within seconds hit near 120%. The pilot reported that diagnosis was extremely difficult, due to the high airframe vibration, making the panel near impossible to read. In fact due to the shake could not ensure which engine went high. The result was engine meltdown, resulting in fire, which then gave the pilot an engine to work with. All this in a matter of less that 10 seconds. He managed to land the aircraft safely to an offshore location. The result was an engine destroyed, engine deck delamination due to vibration, drive train was damaged, and from what I was told the rotor blades measured 25mm longer than standard, so it sure wound up. As an aside the management and engineering of the company involved tryed to crucify the pilot, who was alone ( not 2 pilot) They said he must have placed the fuel govenor switch to manual to cause such overfuelling. He was later exonerated by Pratt and whitney who upon tearing the engine down found the root cause.
His reported way of dealing with the situation as it happened was to immediately pull collective to try an hold back the rapidly rising Nr. In the short time the engine was on fire so that he dealt with as per 412 manual. He said there was no time, and indeed great difficulty, to diagnose because of the high vibration he experienced. I suppose this was due to a severely out of balance roter system at the quickly rising Nr.
The guy was a very experienced 412 pilot, and was in his words lucky that the fire occured before the drive train or rotor system came adrift.
His reported way of dealing with the situation as it happened was to immediately pull collective to try an hold back the rapidly rising Nr. In the short time the engine was on fire so that he dealt with as per 412 manual. He said there was no time, and indeed great difficulty, to diagnose because of the high vibration he experienced. I suppose this was due to a severely out of balance roter system at the quickly rising Nr.
The guy was a very experienced 412 pilot, and was in his words lucky that the fire occured before the drive train or rotor system came adrift.
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Yabu,
I'll bet that was a handful, and the pilot did very well, but I'll also bet it was worse than you described. The auto-accel is a term we use to describe how an engine runs away when a flammable liquid is poured into the engine (usually by a bad bearing seal or an oil leak in the engine inlet). In these cases, the oil that pours into the engine is a good fuel source, and the fuel control is of no help, since it an only cut back the legitimate fuel, while the "new" fuel source is uncontrolled and usually very much more than the engine needs. For example, if you dribble oil into the inlet at 2 ounces per second, the engine will speed up to give you takeoff power!
What your friend experienced was probably a bearing failure on the engine internal shaft, which allowed bearing lubricant oil to leak into the internal air path of the engine, driving it to well above max power. The vibration was that poor engine running with one internal shaft bearing gone, so that engine shaft was whipping like crazy. The fire is because the engine finally split open and the hot gases poured into the compartment and attempted to prove the rating of the fire zone.
Corrective action = pull collective to keep the rotor in the green, shut that engine down (but it won't really shut down until it runs out of oil!) and get ready for a shaft failure/engine fire or something like that. Your friend gets an A++ on that check ride!
I'll bet that was a handful, and the pilot did very well, but I'll also bet it was worse than you described. The auto-accel is a term we use to describe how an engine runs away when a flammable liquid is poured into the engine (usually by a bad bearing seal or an oil leak in the engine inlet). In these cases, the oil that pours into the engine is a good fuel source, and the fuel control is of no help, since it an only cut back the legitimate fuel, while the "new" fuel source is uncontrolled and usually very much more than the engine needs. For example, if you dribble oil into the inlet at 2 ounces per second, the engine will speed up to give you takeoff power!
What your friend experienced was probably a bearing failure on the engine internal shaft, which allowed bearing lubricant oil to leak into the internal air path of the engine, driving it to well above max power. The vibration was that poor engine running with one internal shaft bearing gone, so that engine shaft was whipping like crazy. The fire is because the engine finally split open and the hot gases poured into the compartment and attempted to prove the rating of the fire zone.
Corrective action = pull collective to keep the rotor in the green, shut that engine down (but it won't really shut down until it runs out of oil!) and get ready for a shaft failure/engine fire or something like that. Your friend gets an A++ on that check ride!
Yabu,
I had heard that story - and apparently it happened again some three months after the first, again on a 412 in the middle east. I just hope that when something like that happens to me, that I can get out of it as well as your mate - what a great job. I heard that on the second one, that engine fire illuminated the T handle on the dash, and that was about all the pilot could see due to the vibrations, so he pulled it and solved the problem!
Nick,
I think we all agree on your methodology, and I note that you say that NR high is "probably" a high side, NR low is "probably" a low side. I believe that retarding the high engine will always give you a more accurate diagnosis with a high side, low side or torque split- and it is usually the diagnosis that gets you because most pilots can fly the NR successfully.
I had heard that story - and apparently it happened again some three months after the first, again on a 412 in the middle east. I just hope that when something like that happens to me, that I can get out of it as well as your mate - what a great job. I heard that on the second one, that engine fire illuminated the T handle on the dash, and that was about all the pilot could see due to the vibrations, so he pulled it and solved the problem!
Nick,
I think we all agree on your methodology, and I note that you say that NR high is "probably" a high side, NR low is "probably" a low side. I believe that retarding the high engine will always give you a more accurate diagnosis with a high side, low side or torque split- and it is usually the diagnosis that gets you because most pilots can fly the NR successfully.
Nick, 2 probs with your theory:
1. Don't have another pilot to 'share the blame with'!
2. Don't have throttles!! Just switches from Flight to GI!!
Otherwise ....agree with you!
1. Don't have another pilot to 'share the blame with'!
2. Don't have throttles!! Just switches from Flight to GI!!
Otherwise ....agree with you!
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helmet fire,
I suggest that you not grab the high torque engine if its brother engine has quit. If you always grab the high engine, you will be wrong about 90% of the time, because if engine failures are rare, high side failures are much more so.
I strongly suggest doing nothing, because you really don't have to do anything for a while, and then grab the proper lever and test your theory slowly.
I suggest that you not grab the high torque engine if its brother engine has quit. If you always grab the high engine, you will be wrong about 90% of the time, because if engine failures are rare, high side failures are much more so.
I strongly suggest doing nothing, because you really don't have to do anything for a while, and then grab the proper lever and test your theory slowly.
Nick,
thanks for that advice - I'll try not to grab the only live engine.....
We are ALL suggesting that slowly slowly approach, but I guess it never hurts to repeat that mantra.
It's interesting that 90% of governor failures are low side - I thought the vast majority were designed to fail high, and I must confess that the vast majority I have heard of have been high. None the less, grabbing the high engine is a diagnostic tool - not a solution. Of course to be used slowly.
thanks for that advice - I'll try not to grab the only live engine.....
We are ALL suggesting that slowly slowly approach, but I guess it never hurts to repeat that mantra.
It's interesting that 90% of governor failures are low side - I thought the vast majority were designed to fail high, and I must confess that the vast majority I have heard of have been high. None the less, grabbing the high engine is a diagnostic tool - not a solution. Of course to be used slowly.
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helmet fire,
I didn't mean to imply that low side failures are more common. I think you are right, many governor failures are up, but all goveror failures are rare. The problem we see is that the common, garden variety engine failure creates a big torque split, and can be (and often is) mistaken for a high side failure of the opposite engine, with dsasterous results.
When I first checked out in twin helicopters, I found an entire school of pilots who were being taught to grab the engine levers at the outset, so that they were primed to do something with them. It is my earnest belief that the levers could be locked out for the first minute of any torque split emergency without creating a big safety change. Of course, other emergencies require their quick manipulation (fires, anti-torque failures, rapid shutdowns on the deck) so we must leave them in plane sight, but when one engine is acting strange, there is a disappointing percentage of time when the crew jumps too quickly and grabs the wrong one.
I didn't mean to imply that low side failures are more common. I think you are right, many governor failures are up, but all goveror failures are rare. The problem we see is that the common, garden variety engine failure creates a big torque split, and can be (and often is) mistaken for a high side failure of the opposite engine, with dsasterous results.
When I first checked out in twin helicopters, I found an entire school of pilots who were being taught to grab the engine levers at the outset, so that they were primed to do something with them. It is my earnest belief that the levers could be locked out for the first minute of any torque split emergency without creating a big safety change. Of course, other emergencies require their quick manipulation (fires, anti-torque failures, rapid shutdowns on the deck) so we must leave them in plane sight, but when one engine is acting strange, there is a disappointing percentage of time when the crew jumps too quickly and grabs the wrong one.
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If it wasn't an engine failure in a single engine helicopter, the best advice I was given was 'reach out and wind the clock'.
'Course, now that we have digital clocks....
'Course, now that we have digital clocks....
