donnlass

Watching a Fedex 767 pushback in Dublin and after clearing the truck and starting up the engines, there was a load of blue smoke came out of the engine but no one looked too alarmed and it went on its way.


With it looking an old and grubby beast, what could have caused the blue smoke, would it be an oil leak that doesnt stop it flying?

Blink182

The oil seals on modern jet engines are "labarinth" type seals which rely on air pressure to counteract the oil pressure. During start up , you can get the oil pressure coming up quite quickly , way before full balancing air pressure across the seals on the bearings.......so some of the oil leaks across and usually this air is vented to the turbine area so this air/oil mixture ends up at the turbine area where it gets burnt with a momentary puff of smoke.......once the core engine is up to speed the air pressure can counteract the oil pressure and so the smoke doesn't happen.
It sometimes is more obvious if the oil level has been over -serviced.

donnlass

Thanks lots Blink for explaining that, so its a sign of efficient maintenance then

spannersatcx

Or was it unburnt fuel which is quite normal on engine start?

dixi188

I didn't know FEDEX had 767s.

Sure it wasn't a 757?

srobarts

Don't know the date, but looking at the Dublin movements there is a Fedex A-300 there on a daily basis at the moment.

Flightmech

FedEx dont operate the 767 (yet) and the '57 doesn't go to DUB. It would have been a PW powered A300-600. If the engines were cold soaked it's a common characteristic of the PW4000. The PW powered MD-11 does it as well. As the aircraft sits over time the bearing seals lose air pressure and allow oil to seep into the engine or transfer across the seal during inital high oil pressure on start. It also has a generous fuel schedule on start so theres probably a bit of unburnt fuel in there too! Sometimes on the MD-11 after a 50hr+ layover you cant see to push the thing back initially when #3 lights up!

donnlass

You're certainly right on the aircraft type, thanks for correcting me

Thanks for all the other info as well

spottilludrop

More likely worn valve guides/seals i would say

Otto Throttle

Cracked piston ring,

White smoke and the turbo has blown.

Flightmech

Burning off the excess Redex that was put in the FedEx...I'll get my coat

Rollingthunder

There has been progress - "Fifi"


Oh, that didn't work with No.One....let's try No.Three.

Four?

El Grifo

The weird vid-synch thing with the prop rotation for the first 5 mins or so makes it a very boring watch.

You have no idea if the engines have started or if the props are windmilling

onetrack

That starting and warm-up exercise is quite impressive to watch. Makes you realise the amount of effort required from bomber crews in WW2.
The landing involved quite a surprising amount of yaw upon hitting the asphalt. I would have thought that straightening up on touchdown was the mark of a skilled PIC.

I always admired the RAAF blokes dropping the Caribous onto Luscombe Airfield at Nui Dat, which was often done with moderate-to-strong cross-winds.
The substantial yaw was visible to anyone on the ground, but the 161 blokes always straightened up beautifully right about as the wheels touched the tarmac. It was impressive to watch.
I'd guess the low speeds and manouverability of the 'Bou did help in that respect.

Intruder

Depends on the airplane... Some are landed in a crab, some are landed with wing down and top rudder, some are landed with a combination. For most/all, the MOST important thing is to have the velocity vector straight down the runway on touchdown. Heavy airplanes will straighten themselves out if landed in a crab.

While some pilots advocate "kicking out" a crab, that may introduce instabilities that you may not really want on touchdown...