I was flying out of Frankfurt today, and saw a LH A380 over in the maintenance area with thick white smoke coming out of what I assume was one of the engines. Is that the problem part or would this be some post-fix testing?

Greeting from airline maintenance land.
Of course, all we can do is make a guess.
But sometimes when you change an engine component, for example, an FCU/HMU (Fuel Control Unit/Hydro-Mechanical Unit), the preservation oil that the unit is filled with must travel through the fuel system and eventually out the tailpipe during the first run of the installed part.
Other times, after a fuel nozzle has been removed, perhaps for a scheduled borescope inspection, the fuel nozzle must be reinstalled and the system operated. This can emit a white fuel fog out of the tail pipe.

It's possible, but very low on the list of likely items, that what you saw was itself the problem. Wet starts are pretty rare these days, as engine ignition systems are tremendously simple and reliable. But it's theoretically possible.

The amount of smoke associated with the first time an engine is ever started on wing can be truly amazing. Sometimes there is barely any smoke. Other times it can be seem for miles.

Or, they may have been doing a wet motor for a leak check of a component that was replaced or hunting for a leak.

A wet motor is when the engine is turned using the starter, full is introduced, but ignition is disabled (pulling circuit breakers).

Interesting, thanks.

smokeybandit wrote:

I was flying out of Frankfurt today, and saw a LH A380 over in the maintenance area with thick white smoke coming out of what I assume was one of the engines.

Like this?
https://youtu.be/O-FQ7W7W6Ac

BREECH wrote:

smokeybandit wrote:

I was flying out of Frankfurt today, and saw a LH A380 over in the maintenance area with thick white smoke coming out of what I assume was one of the engines.

Like this?
https://youtu.be/O-FQ7W7W6Ac

Yup, "wet start". Continue to motor and watch you EGT if you are going for a start. Completely normal stuff when you hang a new engine on the wing.

It just might have been a Wet Motoring operation checking for leaks with the Ignition off. Then they'll clear the engine by dry motoring with the ignition and Fuel off, And if everything is ok? Then they'll Idle run the engine and possibly go to part power if necessary. Pretty Standard proceedures

I vote for an engine change, looks a little to dense for a wet start. Only time I’ve seen worse than that was after an engine change on a 757 when they accidentally hooked the oil to the fuel and the fuel to the oil — Boeing field went IFR. On the 757 initially, the fuel and oil lines were long enough to go to either and the connectors were the same size — only the markings were different.

quoting stratclub (Reply # 7), "Yup, "wet start". Continue to motor and watch you EGT if you are going for a start."

stratclub, I don't think I understand the concept of a wet start. In Reply # 4, fr8mech describes a wet motor as introducing fuel into the engine but disabling the ignition such that no start occurs, but how does a wet start differ from a normal start? Are you still starting the engine with fuel and ignition?

On the aircraft I fly (CFM-56 engine), using a normal start with FADEC operating, ignition is energized around 17% N2 and fuel is introduced around 23% N2. We also have manual start procedures, but I have not heard of a wet start.

e38

I suspect a “wet start” is when an engine won’t light off on one igniter and the person starting the engine switches to their other (or both) without disengaging the starter. Though, I’ve never heard the term before.

An actual "wet start" could be where the engine fails to accelerate and the result could be a higher than normal EGT and lot's of smoke. The proper name for an engine failing to accelerate is a "hung start". Sorry for the confusion.

No, if you had a failure to light, you would not monkey around with the ignitors, you would cut off fuel and motor to clear the engine of fuel and then investigate. I did see a customer rep forget to push in the ignitor breakers and when he turned on fuel, the fuel flow was good but the engine didn't light. He reached around with fuel still flowing and reset the breakers and there was an explosion that felt like it blew the tail pipe off of the engine.

fr8mech wrote:

I suspect a “wet start” is when an engine won’t light off on one igniter and the person starting the engine switches to their other (or both) without disengaging the starter. Though, I’ve never heard the term before.

Sort of a slang term meaning that there is unburned fuel coming out of the tail pipe.

No, if you had a failure to light, you would not monkey around with the ignitors, you would cut off fuel and motor to clear the engine of fuel and then investigate.

I did see a customer rep forget to push in the ignitor breakers prior to starting and when he turned on fuel, the fuel flow was good but the engine didn't light. He reached around with fuel still flowing and reset the breakers and there was an explosion that felt like it blew the tail pipe off of the engine.

e38 wrote:

quoting stratclub (Reply # 7), "Yup, "wet start". Continue to motor and watch you EGT if you are going for a start."

stratclub, I don't think I understand the concept of a wet start. In Reply # 4, fr8mech describes a wet motor as introducing fuel into the engine but disabling the ignition such that no start occurs, but how does a wet start differ from a normal start? Are you still starting the engine with fuel and ignition?

On the aircraft I fly (CFM-56 engine), using a normal start with FADEC operating, ignition is energized around 17% N2 and fuel is introduced around 23% N2. We also have manual start procedures, but I have not heard of a wet start.

e38

There IS no wet start! If you delay the ignition on a normal start then what you might have is a FIRE.. if you're leak checking the engine for any reason what you're looking for is fuel leaks at components and connections without pouring the coals to the engine. and after Wet motoring the engine it would be wise to dry motor the engine to clear excessive fuel from the engine before attempting a normal start. Can you do it? Yes you can. Should you do it? Not really.

strfyr51 wrote:

e38 wrote:

quoting stratclub (Reply # 7), "Yup, "wet start". Continue to motor and watch you EGT if you are going for a start."

stratclub, I don't think I understand the concept of a wet start. In Reply # 4, fr8mech describes a wet motor as introducing fuel into the engine but disabling the ignition such that no start occurs, but how does a wet start differ from a normal start? Are you still starting the engine with fuel and ignition?

On the aircraft I fly (CFM-56 engine), using a normal start with FADEC operating, ignition is energized around 17% N2 and fuel is introduced around 23% N2. We also have manual start procedures, but I have not heard of a wet start.

e38

There IS no wet start! If you delay the ignition on a normal start then what you might have is a FIRE.. if you're leak checking the engine for any reason what you're looking for is fuel leaks at components and connections without pouring the coals to the engine. and after Wet motoring the engine it would be wise to dry motor the engine to clear excessive fuel from the engine before attempting a normal start. Can you do it? Yes you can. Should you do it? Not really.

You are correct. Wet motor is the correct term for what I meant. No you would not delay ignition for any reason and if you did a wet motor you would shut off fuel and continue to motor to clear the engine of fuel, stop motoring, check for evidence of leaks. No leaks? Close up the engine, push in the ignitor breakers and do a normal start.

You would not have a fire if you delayed ignition, you would have an explosion. See my example in post 13.

I remember watching TWA L1011 starts at LAX. Hello smoke.

In cold, and not-so-cold, weather JT9D engines were nortorious for ‘fogging’ before lighting off. You’d get a gentle ‘whoof’ when it lit off, along with the possibility of a small fireball.

In maintenance, we would start the engines holding one ignitor in ‘ground’ and the other in ‘flight’. It seemed to minimize the ‘whoofing’.

fr8mech wrote:

I suspect a “wet start” is when an engine won’t light off on one igniter and the person starting the engine switches to their other (or both) without disengaging the starter. Though, I’ve never heard the term before.

It used to happen on the DC-9 series a/c quite often usually with mechanics but I've seen a pilot do it too they would do the start sequence and throw the fuel lever and forgot they didn't have the ignition on and hit the ignition and boom large flame thrower out the tailpipe. You always knew when you saw the fog you were either going to get a torch or they caught it in time and were motoring the engine to get the excess fuel out.