757.packs smelling on FL400 ferry
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757.packs smelling on FL400 ferry
757 ferry flight at FL400, SAT -55 degrees C, oldest aircraft in the fleet.
About 2 mins after top of climb there was a smell of hot plastic in the rear that, after contact with engineering on HF, was mostly resolved by placing the trim air off and packs to stby-C. Smell departed but temps dropped to about 8 centigrade.
Anyone have any tech info on what was happening? I ASSUME that a lack of pax meant that the heat exchangers were struggling to get enough heat into the fuselage without 235 pax generating heat and thus got overworked.
Not seen this described elsewhere but eng say it has happened before. Nearly dropped into Dubrovnik for a night out!!
About 2 mins after top of climb there was a smell of hot plastic in the rear that, after contact with engineering on HF, was mostly resolved by placing the trim air off and packs to stby-C. Smell departed but temps dropped to about 8 centigrade.
Anyone have any tech info on what was happening? I ASSUME that a lack of pax meant that the heat exchangers were struggling to get enough heat into the fuselage without 235 pax generating heat and thus got overworked.
Not seen this described elsewhere but eng say it has happened before. Nearly dropped into Dubrovnik for a night out!!
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The burnt plastic smell on the 757 is due to contamination of engine bleed air with engine oil. At low power settings the engines produce insufficient bleed air using the low pressure bleed so additional higher pressure air is used to provide sufficient flow to maintain pressurisation.
The bleed air is at very high temperature and the heat exchangers cool the air they don't heat it.
I suspect that there is a small oil seepage somewhere in the high pressure section of one of the engines
The bleed air is at very high temperature and the heat exchangers cool the air they don't heat it.
I suspect that there is a small oil seepage somewhere in the high pressure section of one of the engines
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I've had to solve lots of oil smells in the cockpit of 757's (RR engines). They mostly occur after TOC indeed. You can easily do some troubleshooting on that by switching off left or right packs. If you have smells with left pack off, it's the right engine that looses some oil.
An engineer can tell this most of the time by removing the spinner cone. Inside there is a tube for hot bleed air (anti ice), and if oil gets in the bleed air, there will be a small puddle of oil inside the spinner. If oil is found engineers will do a ground full power run and check the whole bleed air system. If they also smell it, most probably the engine will be replaced.
You can get oil seepage via the bearings of the engine shafts, they are pressurized by bleed air. Then the smell occurs during engine oil overfill, or with old bearings (as you describe your aircraft as the oldest of the fleet?) We have a company procedure in place that orders us to fill engine oils to 16-17, NEVER to 20-20. That's however a one time Rolls Royce-Boeing-Company agreement because we fly small sectors.
However, if you say it is really a plastic smell, I've only had that once, a mechanic replaced a bleed tube, but did not know some plastic was inside the new one. But then, you would have smells during the whole flight, not only after toc. So, check also if recently a tube was replaced in the trim air system?
An engineer can tell this most of the time by removing the spinner cone. Inside there is a tube for hot bleed air (anti ice), and if oil gets in the bleed air, there will be a small puddle of oil inside the spinner. If oil is found engineers will do a ground full power run and check the whole bleed air system. If they also smell it, most probably the engine will be replaced.
You can get oil seepage via the bearings of the engine shafts, they are pressurized by bleed air. Then the smell occurs during engine oil overfill, or with old bearings (as you describe your aircraft as the oldest of the fleet?) We have a company procedure in place that orders us to fill engine oils to 16-17, NEVER to 20-20. That's however a one time Rolls Royce-Boeing-Company agreement because we fly small sectors.
However, if you say it is really a plastic smell, I've only had that once, a mechanic replaced a bleed tube, but did not know some plastic was inside the new one. But then, you would have smells during the whole flight, not only after toc. So, check also if recently a tube was replaced in the trim air system?
Last edited by Piper19; 7th May 2008 at 12:45.
Thread Starter
I know the oil smell (OH BOY, do I know it!!!!!) and it was very different this time. Think 1970's British car wiring loom short-circuit smell and you'd be about right. Acrid PVC smell, no 'blue haze' as you get when the RB211 oils the bleed system and it hurt the eyes and throat, which the oil doesn't immediately do.
I suffered a massive oil-out some years ago where the haze was so thick that it remained IMC in the flightdeck for 25 mins after chocks.
So.....how hot is bleed air when it exits the engine? I'd assumed that the eng info was correct and that the bleed air was overheating something since the punkalouvre (sp?) ducts above the front galley were pushing out hot air instead of the normal cooling blast.
PS Ground tested. Satis
I suffered a massive oil-out some years ago where the haze was so thick that it remained IMC in the flightdeck for 25 mins after chocks.
So.....how hot is bleed air when it exits the engine? I'd assumed that the eng info was correct and that the bleed air was overheating something since the punkalouvre (sp?) ducts above the front galley were pushing out hot air instead of the normal cooling blast.
PS Ground tested. Satis
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I promise that 757 packs do not overwork on ferry flights. I ferry empty 757s just as much as I fly full ones, and never has there been an overworked pack problem.
Two other possible causes of burning smells we have experienced in the 757:
1. Dust accumulation on top of the standby inverter begins to heat up and smolder, causing an unidentifiable source of smoke and a foul smell. Resulted in a diversion and a lot of pilot sweating over the Indian Ocean.
2. Electrical arcing on the screw connecting the window-heat power wires to the forward windows. Those screws are supposed to have a plastic cap on them, but sometimes the caps fall off and the screw is exposed. The arcing is enough to cause a very objectionable smell and two diversions so far, until the cause was finally discovered. Another note: that bare screw would really give you a jolt if you touched it with a metal clipboard by accident.
Two other possible causes of burning smells we have experienced in the 757:
1. Dust accumulation on top of the standby inverter begins to heat up and smolder, causing an unidentifiable source of smoke and a foul smell. Resulted in a diversion and a lot of pilot sweating over the Indian Ocean.
2. Electrical arcing on the screw connecting the window-heat power wires to the forward windows. Those screws are supposed to have a plastic cap on them, but sometimes the caps fall off and the screw is exposed. The arcing is enough to cause a very objectionable smell and two diversions so far, until the cause was finally discovered. Another note: that bare screw would really give you a jolt if you touched it with a metal clipboard by accident.
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I feel for the poor guy at the overhaul shop. I've had to investigate several 535 oil smell enignes, when they are torn down you can see nothing obviously wrong with them. You just have the re-line all the oil/air seals, replace the oil pump for a new unit and off you go again. One particular engine failed 3 times before we fixed it.
TWApilot - interesting point about those screws - anybody know of any a/c type doing this?
Regards,
N1 Vibes
TWApilot - interesting point about those screws - anybody know of any a/c type doing this?
Regards,
N1 Vibes
Buttonpusher
Anyone had occasion on the 757's to enjoy the smell of slime coming from the packs (or something like slime) on descent into hot/humid conditons at relatively low altitudes like 2-3000' for example as in Florida ?? The story at my airline is it's built up fungus, but I'd like a more definitive answer. TIA FLCH
