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LVPlanefan
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Joined: Sat May 07, 2005 9:07 am

Fuel And Oil Odors During Flight

Thu May 04, 2006 10:31 am

On two recent flights I took I noticed an odor coming out of the overhead a/c nozzles that smelled like either engine oil or jet fuel (or jet exhaust). It only lasted 30 seconds and happened when the engines were at cruise or near idle on descent. It then reappeared minutes later. This only happened when I sat over the wings near the engines. These were both A320 and B737NG aircraft. The first time I smelled this I became quite alarmed and thought there was a possible fire.
Could a pilot or mechanic tell me if this is normal and explain why this happens to help me calm my nerves for future flights. Thanks!!
 
SFOMB67
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RE: Fuel And Oil Odors During Flight

Thu May 04, 2006 2:35 pm

I wouldn't say it's normal. Quite often, on the ground you smell jet exhaust from a plane in front of you, as your plane's A/C system sucks it in. I can only think it could have been an oil smell from something leaking in the A/C packs. Don't know how exhaust fumes would get in the A/C system in cruise.
Not as easy as originally perceived
 
Tristarsteve
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RE: Fuel And Oil Odors During Flight

Thu May 04, 2006 4:18 pm

The air you breath in the cabin in nearly all jet aircraft is bled from the engine compressor. The bearings in the engines have pressurised oil in them. The engine manufacturers do a good job in keeping the engine oil from getting into the air path and then into the cabin, but it happens. Especially on older aircraft a whiff of oil when the packs are turned on at engine start was quite normal. Also at Top of Descent, the engines are throttled back to idle. As the air pressure in the bleed offtake drops, the HP valve opens to let Hot HP air into the bleed system. On some aircraft you can hear this happening. On the Tristar it was very prominent, a sort of whoosh as each HP valve opens. This can also bring a whiff of hot oil into the cabin.
But if the smell continues, then there is a problem. The B757 and Avro 100 are well known offenders.
The only way to get fuel or exhaust smell in is when you are on the ground queing for departure. The wind will blow the exhaust to the front of the engine and it will be drawn back in again, and then out through the bleed system. It can get quite strong on a windy day.
 
troubleshooter
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RE: Fuel And Oil Odors During Flight

Thu May 04, 2006 4:28 pm

The BAe146 smells like hell in the morning if you run the packs with APU bleed air prior the first flight of the day. Leaks on the bearing seals inside the APU let oil enter the compressor section and is then in the bleed supply system to the A/C packs. Sometimes even the flight crews complaint about headache due to this smell.
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Airmech56
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RE: Fuel And Oil Odors During Flight

Thu May 04, 2006 7:50 pm

Also in 737 NG, fan lubes are performed,( at least the airline that I work for,im not sure what other airlines do), in which the fan blades and all attaching hardware is cleaned and lubricated to prevent or fix engine vibration, and one of the tasks performed after instalation is to run the engine at 85% with the packs on to get rid of any smell or smoke that any residual lube may cause by the centrifugal force of the fan. This task was added later on, as there were many reports by passengers of strong fuel like smell, and/or smoke in the cabin.
 
kaddyuk
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RE: Fuel And Oil Odors During Flight

Thu May 04, 2006 8:23 pm

Quoting Airmech56 (Reply 4):
Also in 737 NG, fan lubes are performed,( at least the airline that I work for,im not sure what other airlines do), in which the fan blades and all attaching hardware is cleaned and lubricated to prevent or fix engine vibration, and one of the tasks performed after instalation is to run the engine at 85% with the packs on to get rid of any smell or smoke that any residual lube may cause by the centrifugal force of the fan. This task was added later on, as there were many reports by passengers of strong fuel like smell, and/or smoke in the cabin.

Uh-Huh... i've done the same on the CFM56-5B and the RR Trent 556... Using Molycote i think...
Whoever said "laughter is the best medicine" never had Gonorrhea
 
AvionicMech
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RE: Fuel And Oil Odors During Flight

Thu May 04, 2006 9:20 pm

Quoting Airmech56 (Reply 4):
Also in 737 NG, fan lubes are performed,( at least the airline that I work for,im not sure what other airlines do), in which the fan blades and all attaching hardware is cleaned and lubricated to prevent or fix engine vibration, and one of the tasks performed after instalation is to run the engine at 85% with the packs on to get rid of any smell or smoke that any residual lube may cause by the centrifugal force of the fan. This task was added later on, as there were many reports by passengers of strong fuel like smell, and/or smoke in the cabin.

Yeah we quite regularly do fan blade lubes if the aircraft is having a bit of a problem with n1 vibe. But I don't think I have ever seen anyway run the engines up and put the packs on the take out any smell.

Wouldn't it be better to switch the engine bleeds off before start up and then run them up to 85% for a certain amount of time so that the lube doesn't get passed into the pneumatic system in the first place? Then maybe after a couple of mins at highish power to turn the bleeds on with the packs and see if it smells then?
 
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nonfirm
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RE: Fuel And Oil Odors During Flight

Fri May 05, 2006 5:10 am

Quoting Airmech56 (Reply 4):
Also in 737 NG, fan lubes are performed,( at least the airline that I work for,im not sure what other airlines do), in which the fan blades and all attaching hardware is cleaned and lubricated to prevent or fix engine vibration, and one of the tasks performed after instalation is to run the engine at 85% with the packs on to get rid of any smell or smoke that any residual lube may cause by the centrifugal force of the fan. This task was added later on, as there were many reports by passengers of strong fuel like smell, and/or smoke in the cabin.

Do you spray the molycote or do you brush it.We have had the smell problem on the ng fleet and after t/s over a few days on two of the airplanes it ended up being the ozone converter bad.
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LVPlanefan
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RE: Fuel And Oil Odors During Flight

Fri May 05, 2006 7:23 am

Actually, come to think of it, it was a more of a sharp menthol type smell..kind of like a really strong cough drop. I noticed it also on the ground at engine start, but then I smelled it again during flight, and this happened on more than one flight.
 
dl757md
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RE: Fuel And Oil Odors During Flight

Fri May 05, 2006 8:56 pm

Quoting AvionicMech (Reply 6):
Wouldn't it be better to switch the engine bleeds off before start up and then run them up to 85% for a certain amount of time so that the lube doesn't get passed into the pneumatic system in the first place? Then maybe after a couple of mins at highish power to turn the bleeds on with the packs and see if it smells then?

That's the way we do it where I work. Well actually we do the whole run with the bleeds off. After we taxi to the run-up area we run at 80%N1 for 5 mins. to heat soak the engine and then do a 2 minute min. up and 2 minute min down idle-TO-idle vibration survey per test 7 and note peak vibes and their corresponding N1 and N2 values. If they aren't good we do a test 7 imbalance data run so the AVM will give us a solution to add/remove fan balance weights.

We've done close to 400 (ours are on a 1500hr lube cycle) CFM56-7 fan lubes at our station using the above procedures and have never had fan lube induced cabin odor problems.

Quoting Nonfirm (Reply 7):
Do you spray the molycote or do you brush it.

We use G/N metal paste brushed on per the EMM.

DL757Md
757 Most beautiful airliner in the sky!
 
dl757md
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RE: Fuel And Oil Odors During Flight

Fri May 05, 2006 9:22 pm

Quoting LVPlanefan (Reply 8):
Actually, come to think of it, it was a more of a sharp menthol type smell..kind of like a really strong cough drop. I noticed it also on the ground at engine start, but then I smelled it again during flight, and this happened on more than one flight

Probably Skydrol then. Very low concentrations of Skydrol vapors may have an odor that could possibly be described as "sharp". Higher concentrations would be described as burning or tear gas like.

DL757Md
757 Most beautiful airliner in the sky!
 
Airmech56
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RE: Fuel And Oil Odors During Flight

Fri May 05, 2006 9:23 pm

Alright, let me clear this up for anyone who doesnt know.

1- Fan lube is performed ( its a paste, we apply it with a brush)
2- We run the engine with the packs off at 4 different N1 speeds all the way to take off, so as to give the AVM ( airborn vib monitoring) a solution as to where to add or remove balance weights, if necessary. This takes about 20 minutes.
3- Then after we fix the vib, we then run the engine all the way up to 85% for 5 minutes with the packs on to get rid of any smell.
 
jeb94
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RE: Fuel And Oil Odors During Flight

Mon May 08, 2006 11:54 am

On aircraft with clam shell type thrust reversers you can get exhaust gases deflected forward and have them ingested through the inlets during landing. On the MD-80 the A/C packs are supposed to shutdown when the TR's are deployed for this reason. Sometimes it succeeds, sometimes it doesn't.
 
Tristarsteve
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RE: Fuel And Oil Odors During Flight

Mon May 08, 2006 6:00 pm

Quoting Dl757md (Reply 10):
Probably Skydrol then

The hydraulic tanks are pressurised with air from the same pneumatic system that supplies the air conditioning packs. If the tanks are overfull (by fluid transferring from tank to tank due to an internal leak somewhere) then skydrol can get into the pneumatic system and therfore into the cabin.
Not very common.
 
ballpeeen
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RE: Fuel And Oil Odors During Flight

Mon May 08, 2006 6:10 pm

uhh...dirty coalescer filter, anyone?
 
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HAWK21M
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RE: Fuel And Oil Odors During Flight

Mon May 08, 2006 7:40 pm

Quoting TristarSteve (Reply 2):
The B757 and Avro 100 are well known offenders.

Which Engines RR or P&W on the B757s.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Tristarsteve
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RE: Fuel And Oil Odors During Flight

Mon May 08, 2006 8:02 pm

Quoting HAWK21M (Reply 15):
Which Engines RR or P&W on the B757s

RR.
There was a very long thread about it on Pprune a few months ago.
 
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HAWK21M
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RE: Fuel And Oil Odors During Flight

Fri Jun 09, 2006 2:37 am

I've noticed this recently.It can be caused if Oil Quantity is Overfilled.
On RB211-535Cs We Maintain 18qts & 19qts respectively on LH & RH sides.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
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HAWK21M
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RE: Fuel And Oil Odors During Flight

Tue Jun 05, 2007 5:31 pm

I read an article on another forum commenting on the Oil odours in flight on the B752s & specially mentioned the RB211-535C.
How is the RB211-535E4 in this regard.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
N231YE
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RE: Fuel And Oil Odors During Flight

Wed Jun 06, 2007 12:19 am

Interesting...I've noticed the smell of hot oil in the gasper outlets and never really gave much thought as to why. The DC-9 has a real particular smell, but you are talking about 40 year-old engine technology (JT8D).

Exhaust in the system sounds completely understandable, A/C sucking fumes off the surface when taxiing.
 
roseflyer
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RE: Fuel And Oil Odors During Flight

Sat Jun 16, 2007 3:55 pm

Quoting TristarSteve (Reply 13):
The hydraulic tanks are pressurised with air from the same pneumatic system that supplies the air conditioning packs. If the tanks are overfull (by fluid transferring from tank to tank due to an internal leak somewhere) then skydrol can get into the pneumatic system and therfore into the cabin.
Not very common.

That's not true on all aircraft. Some are powered by an electric pump.

But still Skydrol can get everywhere and very low concentrations of it smell bad and can be a bad irritant. I'd guess that maybe something was done to the system via maintenance and that there was some skydrol finding its way into the air system. Its a problem that does not have an easy solution. Plenty of people at Boeing have worked to eliminate the problem, but it is hard to detect skydrol in the air.
If you have never designed an airplane part before, let the real designers do the work!
 
movingtin
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RE: Fuel And Oil Odors During Flight

Sun Jun 17, 2007 11:06 pm

Quoting RoseFlyer (Reply 20):
That's not true on all aircraft. Some are powered by an electric pump.

And which A/C use an electric pump to put a head pressure on the Hyd Reservoirs?
 
roseflyer
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RE: Fuel And Oil Odors During Flight

Mon Jun 18, 2007 2:46 am

Quoting Movingtin (Reply 21):
And which A/C use an electric pump to put a head pressure on the Hyd Reservoirs?

The backup/standby system is often electric if my memory serves correctly, so at least one hydraulic resevoir will usually pressurized to 3000psi with an electric pump. On the 737 for example System A receives pressure from two engine-driven hydraulic pumps, one on each engine, and supplies power to operate the flaps, landing gear, nosewheel steering, inboard brakes, ground spoilers, and some of the flight controls. System B receives pressure from two electric motor-driven pumps to operate the outboard brakes and some of the flight controls. The standby system is pressurized by one electric motor-driven pump to operate the rudder and thrust reversers and extend the leading edge devices if system A or B were to fail.

It isn't too uncommon to lose system A or B on the 737. Both systems can run everything necessary. On the 737NG, I only know of one documented case where both A and B went down. You'll know if the standby system is being used since that motor is so incredibly loud and horrible sounding. It just screams when the flaps are being lowered. If you ever hear that sound inside the plane, it's probably a good idea to look around to see where the exits are and to find your life jacket.
If you have never designed an airplane part before, let the real designers do the work!
 
474218
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RE: Fuel And Oil Odors During Flight

Mon Jun 18, 2007 3:04 am

Quoting TristarSteve (Reply 13):
The hydraulic tanks are pressurised with air from the same pneumatic system that supplies the air conditioning packs. If the tanks are overfull (by fluid transferring from tank to tank due to an internal leak somewhere) then skydrol can get into the pneumatic system and therfore into the cabin.
Not very common.

What aircraft uses the pneumatic sytem to pressureize the hydraulic system?

Every aircraft I have worked on has used engine driven pumps.
 
movingtin
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Joined: Sat Oct 21, 2006 1:03 am

RE: Fuel And Oil Odors During Flight

Tue Jun 19, 2007 1:41 am

All I can say is READ THE POST. This is what was said-

Quoting TristarSteve (Reply 13):
The hydraulic tanks are pressurised with air from the same pneumatic system that supplies the air conditioning packs. If the tanks are overfull (by fluid transferring from tank to tank due to an internal leak somewhere) then skydrol can get into the pneumatic system and therfore into the cabin.
Not very common.



To which this post was made after either not reading or understanding the previous-

Quoting RoseFlyer (Reply 20):
That's not true on all aircraft. Some are powered by an electric pump.

Now, I will ask again- Please name 1 airplane that uses an electric pump to supply head pressure to the Hydraulic tanks(reservours)?
 
roseflyer
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RE: Fuel And Oil Odors During Flight

Tue Jun 19, 2007 9:07 am

Quoting Movingtin (Reply 24):
Now, I will ask again- Please name 1 airplane that uses an electric pump to supply head pressure to the Hydraulic tanks(reservours)?

The standby system (3rd hydraulic system) on the 737 is not supplied by the pneumatic system coming off of bleed air or an engine driven pump, but instead is electric. I'm not referring to entire planes that use electric, but rather to specific hydraulic tanks. The standby system tank is very small and is nothing like the A or B system on the 737.

To the best of my knowledge, for aircraft with a RAT, there is usually an electrically powered hydraulic backup system in case all engines fail to provide hydraulic pressure.

I hope that answers your question, and I apologize for being confusing.
If you have never designed an airplane part before, let the real designers do the work!
 
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HAWK21M
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RE: Fuel And Oil Odors During Flight

Wed Jun 20, 2007 8:21 pm

Quoting RoseFlyer (Reply 25):
To the best of my knowledge, for aircraft with a RAT, there is usually an electrically powered hydraulic backup system in case all engines fail to provide hydraulic pressure.

On the B752.The RAT supplies Hydraulics & the HMG supplies Electrics as a Back up.
regds
MEL
I may not win often, but I damn well never lose!!! ;)

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