This was a strange one, wife and I were returning from a trip. I've flown lots of times, and flown on 737 series plenty of times. Pushed back from the gate, the ventilation quieted down, the rumble from the engine starting began, but we happened to be sitting on the side that was starting and saw great plumes of white smoke coming from the #2 engine for several seconds. Then we hear the rumbling slowing down and getting quiet again, clearly the engine was having some kind of problem. The plane had just landed and offloaded before we boarded, so it wasn't like it was a cold engine, and it was plenty warm outside. So we sat for a minute, and the captain got on the intercom and announced they were having trouble getting the #2 engine started. Well, that's comforting. A minute or so later, they tried again, and it started normally without the smokescreen. They started #1 after we had taxied a bit. Any idea what happened? Wife and I were fully expecting we'd be pulling back into the gate and boarding a different plane. I've just never seen smoke like that from a 737 engine, nor experienced a "no start". Usually just a puff when it ignites, and that's it.
Any turbine experts? Strange 737-700 flight
- Thread starter Dave Sherman
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Last time I flew for business was a 737 (with winglets according to the ticket).
Taxiied to the runway, and just as the turn onto the runway was being finalised, and the Captain starting giving it the berries, engines started to roar plane started to surge, then backed off and turned right off the runway.
Captain reported a "Check Engine Light" on the RHS engine, and a few runs of some checksheets to see if all clear, a few more RPM increases from the engines, and back to the terminal for 2 hours of ground crew tests, cowls open, truck parked there, people milling around, then a start and run.
I've seen a 25MW G.E. that didn't light off very well, and there was lots of unburned diesel in the white plume.
Taxiied to the runway, and just as the turn onto the runway was being finalised, and the Captain starting giving it the berries, engines started to roar plane started to surge, then backed off and turned right off the runway.
Captain reported a "Check Engine Light" on the RHS engine, and a few runs of some checksheets to see if all clear, a few more RPM increases from the engines, and back to the terminal for 2 hours of ground crew tests, cowls open, truck parked there, people milling around, then a start and run.
I've seen a 25MW G.E. that didn't light off very well, and there was lots of unburned diesel in the white plume.
Others likely have better information, but if the ground time for your aircraft was brief, it could be "rotor bowing". It seems that rotors in large turbofan engines will bow a bit during the cool-down phase and shouldn't be restarted until cooling is uniform and the bowing is eliminated. Perhaps the restart was too soon? The process can be accelerated by spinning the turbine at relatively low revs with APU power.
Or it could be something else...
Or it could be something else...
Engines have 2 igniters, which are NOT just spark plugs, but high energy devices that can reliably light off kerosene. They don't last long when used continuously. So they are used just for start and during certain other critical times, such as during heavy rain. Often the engine is configured to use just one igniter during start.
Once the engine is started, the single igniter shuts off. As the combustion chamber maintains combustion reliably. Much like a kitchen stove.
On some engines, If one igniter fails to operate, every other start will fail. As they alternate igniters during every other start. Fuel is simply blown out the tailpipe it it fails to light off. A Zippo lighter thrown into the plume can sometimes light it off, leading to a nice torch.
https://goo.gl/images/k67YAd
Once the engine is started, the single igniter shuts off. As the combustion chamber maintains combustion reliably. Much like a kitchen stove.
On some engines, If one igniter fails to operate, every other start will fail. As they alternate igniters during every other start. Fuel is simply blown out the tailpipe it it fails to light off. A Zippo lighter thrown into the plume can sometimes light it off, leading to a nice torch.
https://goo.gl/images/k67YAd
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Sounds like a hung start.
Propflux01
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Ignitor or excitor problem to me. If both are used for start, one side probably didn't function. The white smoke was the unburned Jet A plume.It happens, AS long as it finally lit off it was good to go.
Originally Posted by Cujet
A Zippo lighter thrown into the plume can sometimes light it off, leading to a nice torch.
Speaking of Zippos and torches, back when they allowed everything on airplanes a guy was sitting next to me in the window seat, wearing a grey wool suit. He was nervously fiddling around with his Zippo lighter which he must has filled with lighter fluid earlier that day. The lighter fluid fumes were strong. He was holding the lighter in his lap and decided to light it. The lighter fluid fumes that permeated his suit lit up and for a second the human torch was sitting next to me in a jet liner. Luckily they burned out and the guy was OK. I wished he would have been outside trying to start the engine in his grey suit.
A Zippo lighter thrown into the plume can sometimes light it off, leading to a nice torch.
Speaking of Zippos and torches, back when they allowed everything on airplanes a guy was sitting next to me in the window seat, wearing a grey wool suit. He was nervously fiddling around with his Zippo lighter which he must has filled with lighter fluid earlier that day. The lighter fluid fumes were strong. He was holding the lighter in his lap and decided to light it. The lighter fluid fumes that permeated his suit lit up and for a second the human torch was sitting next to me in a jet liner. Luckily they burned out and the guy was OK. I wished he would have been outside trying to start the engine in his grey suit.
Sounds like an expected (not normal, but not unusual) start. An aviation jet engine (turbine) is basically just a giant furnace, not much different from the one in your home, not very complex, with a turbine in the furnace exhaust plume, very complicated, high precision unit. The start part of the operation is a fairly primitive "put match to fire" process, with some high reliability parts in place of the match.
Jet A and Jet B (aka "Aviation Kerosenes") are often referred to as kerosene but jet fuels have naptha and other high evaporation fuels in them so that they light easier than straight kerosenes. If you put jet fuel in a pail and come back after some time the aeromatics will have evaporated away and what you are left with is basically conventional kerosene, almost identical to home furnace fuel. If you've ever light a pilot light in a kersene-based heater, you know how difficult it is to get just evaporation from kerosene in the right air-fuel ratio to light easily, thus the aromatics in Jet fuel.
None the less, sometimes the fuel is reluctant to light. Because the "furnace" part is fairly robust and simple in operation, it rarely fails in any non-repairable way (usually just replace the ignitors). Multiple start attempts wont damage anything and the turbine part is more-or-less just along for the ride. Once the fire is lit and they start spooling up then they become important part of the process.
Jet A and Jet B (aka "Aviation Kerosenes") are often referred to as kerosene but jet fuels have naptha and other high evaporation fuels in them so that they light easier than straight kerosenes. If you put jet fuel in a pail and come back after some time the aeromatics will have evaporated away and what you are left with is basically conventional kerosene, almost identical to home furnace fuel. If you've ever light a pilot light in a kersene-based heater, you know how difficult it is to get just evaporation from kerosene in the right air-fuel ratio to light easily, thus the aromatics in Jet fuel.
None the less, sometimes the fuel is reluctant to light. Because the "furnace" part is fairly robust and simple in operation, it rarely fails in any non-repairable way (usually just replace the ignitors). Multiple start attempts wont damage anything and the turbine part is more-or-less just along for the ride. Once the fire is lit and they start spooling up then they become important part of the process.
Wet start.
Second attempt used both sets of igniters and it started normally.
Second attempt used both sets of igniters and it started normally.
I'm often amused at how often our high techology, ultra reliable machines, such as a jet engine, still often come back to the simple process of get something hot, start fire when it comes time to get the whole thing working...
As noted by others above, while not the "typical" start noted in the majority of start events, it isn't abnormal either.
As noted by others above, while not the "typical" start noted in the majority of start events, it isn't abnormal either.
By the way, this is "strange" for the OP.
But it's not uncommon. We have to contact maintenance in the event of a wet start, and if the engine starts OK with the ignition selector in both, then we are good to continue the flight.
Hot start = EGT limit exceeded, usually due to excessive fuel flow.
Hung start = Idle RPM* not reached within 120 seconds of start. Will become hot eventually.
Wet start = no EGT rise within 20 seconds of fuel on.
I have experienced a start or two where the engine had fuel on, with no EGT rise for about 20 seconds, and just before the FO went fuel off, we heard a "whumpf" of ignition and the EGT rose rapidly...which makes sense...the FADEC is dumping fuel in there, with no ignition and while some of the fuel is being blown out the turbine as vapor, some is puddling in the combustion section. When it lights off, it really lights off...
*Jet engine RPM isn't a simple thing. With two (or three) turbine/compressor spools, you're looking at several RPM indications. The fan (N1) speed is always much lower at idle than the core (N2) speed. In general,roughly speaking the N2 is up around 60-75% RPM at idle while the fan is at 20-25%. In a triple spool engine, e.g. the Rolls RB211, you're looking at N1, N2, and N3 (core) speeds. Jet engine RPM is displayed in "% of maximum RPM". So, while the max RPM for N1 might be, say 4000 RPM, it's displayed as %, and the N2 max speed might be, say, 8000 RPM, it's also displayed as %.
Takeoff thrust is usually up around 105% RPM.
So, yeah, they idle at 70% of max RPM, at least the core does while on the ground. Not particularly fuel efficient, but you need that much airflow for stable engine operation and to keep hot spots from forming in the exhaust gas path.
But it's not uncommon. We have to contact maintenance in the event of a wet start, and if the engine starts OK with the ignition selector in both, then we are good to continue the flight.
Hot start = EGT limit exceeded, usually due to excessive fuel flow.
Hung start = Idle RPM* not reached within 120 seconds of start. Will become hot eventually.
Wet start = no EGT rise within 20 seconds of fuel on.
I have experienced a start or two where the engine had fuel on, with no EGT rise for about 20 seconds, and just before the FO went fuel off, we heard a "whumpf" of ignition and the EGT rose rapidly...which makes sense...the FADEC is dumping fuel in there, with no ignition and while some of the fuel is being blown out the turbine as vapor, some is puddling in the combustion section. When it lights off, it really lights off...
*Jet engine RPM isn't a simple thing. With two (or three) turbine/compressor spools, you're looking at several RPM indications. The fan (N1) speed is always much lower at idle than the core (N2) speed. In general,roughly speaking the N2 is up around 60-75% RPM at idle while the fan is at 20-25%. In a triple spool engine, e.g. the Rolls RB211, you're looking at N1, N2, and N3 (core) speeds. Jet engine RPM is displayed in "% of maximum RPM". So, while the max RPM for N1 might be, say 4000 RPM, it's displayed as %, and the N2 max speed might be, say, 8000 RPM, it's also displayed as %.
Takeoff thrust is usually up around 105% RPM.
So, yeah, they idle at 70% of max RPM, at least the core does while on the ground. Not particularly fuel efficient, but you need that much airflow for stable engine operation and to keep hot spots from forming in the exhaust gas path.
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Interesting, did not know there was individual control over the multiple ignitors. Makes sense that it was a case that it just didn't ignite, either because of a faulty ignitor or it needed both to get it started. Oh well, did not realize it wasn't that uncommon, and thankfully we did not get delayed if they had to find another plane.
Thought of this thread today.
Start panel, 757 with PW2037, showing ignition set 1, both, or 2. We alternate the ignition set used on each flight.
Start panel, 757 with PW2037, showing ignition set 1, both, or 2. We alternate the ignition set used on each flight.
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