Contrail from just one engine

Mick West

Administrator
Staff member
Posted on Facebook, apparently from yesterday, maybe Montana.



Looks like one engine is out. But there's a faint trail coming from the port engine. What might that be? Residual fuel leak? Aerodynamic? Engine is just on the lowest power setting?
 
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MikeC

Closed Account
Conceivably one engine out, or one engine running at a significantly different EGT margin to the other.

From the small wispy trail if I had to guess I would guess the later - the port engine is running right at the "edge" of contrail producing parameters whereas the starboard one is clearly inside them. But that is just a guess.

What it pretty clearly is not is camera angle obfuscating or combining 2 contrails into one as somethings happens, nor does it appear to be a tail engined aircraft where the contrails combine almost immediately they form - these might seem obvious but I figure it's usually a good idea to mention the obvious at least once :)
 

Mick West

Administrator
Staff member
Yeah, if it is marginal contrail conditions, then and EGT (Exhaust Gas Temperature) of a few degrees higher could mean the mixing line never goes though the water supersaturate region, and contrails will never - or barely - form.

It's a pity there isn't a longer video where you could see if it came back on, or if the other one went off.
 

George B

Extinct but not forgotten Staff Member
Posted on Facebook, apparently from yesterday, maybe Montana.



Looks like one engine is out. But there's a faint trail coming from the port engine. What might that be? Residual fuel leak? Aerodynamic? Engine is just on the lowest power setting?

Hmmmm . . . Have never seen this situation before. . . Probability of this is rather low. . . .
 
Last edited by a moderator:

PCWilliams

Senior Member.
Yeah, if it is marginal contrail conditions, then and EGT (Exhaust Gas Temperature) of a few degrees higher could mean the mixing line never goes though the water supersaturate region, and contrails will never - or barely - form.

It's a pity there isn't a longer video where you could see if it came back on, or if the other one went off.

We don't know the stage of flight. The aircraft could have just been given a clearance to reduce/increase speed and what we're seeing is a speed transition and the engines are not quite in sync.
 

Mick West

Administrator
Staff member
Hmmmm . . . Have never seen this situation before. . . Probability of this is rather low. . . .

Right, which is why you hardly ever see it. And when you do see it it looks remarkable.

Given that's there's 30,000 commercial flights per day, something with a 1 in a million chance of happening on any given flight will happen ten times a year, somewhere in the US.

How remarkable is it, exactly? 1 in 10,000 flights? 1 in 100,000?

http://www.consumertraveler.com/today/aa-in-flight-engine-problems/
 

PCWilliams

Senior Member.
Last edited by a moderator:

Mick West

Administrator
Staff member
Following your links Jay, i wound up at this page: Contrail pictures of three engined airliners

In many of these pictures the center engine is not producing a contrail.

Or not appearing to at least. In several photos the contrail would be off the side of the photo, or lined up with another contrail.

It does not seem like there's a great practical reason to have three engines though. I wonder if the third engine was treated significantly differently to the main two.

http://en.wikipedia.org/wiki/Trijet
 

PCWilliams

Senior Member.
Or not appearing to at least. In several photos the contrail would be off the side of the photo, or lined up with another contrail.

It does not seem like there's a great practical reason to have three engines though. I wonder if the third engine was treated significantly differently to the main two.

http://en.wikipedia.org/wiki/Trijet

If i remember correctly from my one time flying in the cockpit of a DC-10, once at cruise, they pulled back on the center engine.
 

TWCobra

Senior Member.
Sorry, but they would not do that. If an airliner has three engines then it needs the thrust from all three for normal operations.
 

Mick West

Administrator
Staff member
Sorry, but they would not do that. If an airliner has three engines then it needs the thrust from all three for normal operations.

But does the trust from all three need to be the same? All three engines do not need to operate at full power during normal cruise speed. Or more specifically, does the exhaust gas temperature of the middle engine need to be the same as for the wing engines?
 

MikeC

Closed Account
I know that Maritime patrol aircraft often throttle back or even shut down 1 engine on each wing when patrolling (from ex P3 pilots I have worked with). There woudl be good economic erasons for not running 1 engine if you could do so - engine hours are the prime determinate of engine wear and maintenance requirements.

That said shutting down an engine risks it not restarting (as often happens with APU's and is a significant problem for ETOPS/EDTO that rely upon the APU as an additional soutrce of electrics, hydraulics and air - they have to do restarts at cruise altitudes to check reliability and report all failures)

However I also work with some older pilots who flew Air NZ DC-10's and they tell me they never shut down the middle engine, nor throttled it any differently to the other 2 - whatever thrust was required was achieved from all engines. Now that's not a large sample - possibly other airlines did differently, possibly the USAF does differently with KC-10's.
 

TWCobra

Senior Member.
All three engines are the same and interchangeable. All engines on all multi engine aircraft are the same. If they are there, they are required for normal ops. The P3 did shut down engine 1 for low altitude loiter ops, but always fired it back up again for climb and cruise.
Having said that, all multi engine AC must be capable of losing one engine at any time after the V1 call on takeoff, but that is a non normal operation. Engines and their ancillaries cost and weigh too much to have an extra on the airframe that is not required.
 

MikeC

Closed Account
Yep. Eg when I worked on BAe-146's (no truth in the rumour that BAe stood for "Bring Another engine...;)) there was a "3-engine ferry" procedure in the manual so that if an engine became unserviceable it could be locked (stopped from rotating to prevent further damage) and the aircraft flown back to a maintenance base (without pax or freight on board!) for replacement. I remember the delight when the Engineering Mgmt realised this (I was QA auditor at the time) - after having to apply for "Special Flight Permits" to do so on a few previous occasions because they hadn't realised it was a "normal" procedure
 

TWCobra

Senior Member.
http://avherald.com/h?article=44f9832e&opt=0

This is not the actual incident because it is the wrong engine, but otherwise the photo fits this. Loss of engine at cruising (read possible contrail altitude) and even fuel dumping as a possible explanation for the smaller trail.
This sort of thing happens regularly. Avherald is a great source of up to date events.
 
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