Reply to: Boeing 777 - it's quite safe as long as you are flying to somewhere warm

[Menelaus]

Boeing / Airbus

Surely though Airbus have the system that someone who I worked with years ago referred to as "Fly By Wire, Die By Fire"?

[DaveB]

So what's needed is a heater for fuel prior to use to make sure optimum temperature is achieved. A small reservoir will also be required I guess for sudden fuel consumption, i.e. landing.

Hard to believe something like this does not already exist, FMEA would have shown this.

This is what the oil/fuel heat exchanger is meant to do. It uses heat from the engine oil to warm the fuel before it it pumped into the engine. Since the engines were being run at idle for prolonged periods the oil wasnt hot enough to warm the fuel properly so residual ice crystals in the fuel made it into the injection system and blocked it.

[Svalbaard]

So when was the last time you went on a flight and had a choice of which plane you went on?

Granted, intercontinental you have a choice of many carriers but internal you'd be hard pushed to have the choice of planes.

[sasguru]

I'm glad these planes all have the same amount of flying hours on the clock.

OK , OK 0.002 is an estimate. And why are the flying hours significant? It's not a metal fatigue problem, is it?
In any case I, for one, would not be worrying over much about flying in a 777-Trent plane.

[Paddy]

The old 747s used to pour condensation in the cockpit while landing. First officer would be using one hand with a chamois to wipe the bay windows with other on the throttle.

[scooterscot]

Wonder where the affected aircraft got their fuel from.

[scooterscot]

being conservative, 1000 flights?
And yet there have been only 2 events (Delta and BA)? So there is 0.002 probability of an event in any particular journey.
I wouldn't worry about odds of that nature.

I'm glad these planes all have the same amount of flying hours on the clock.

[sasguru]

Something's not quite right here. The US safety board used the words "high probability" for another event. Yet 777s with Trent engines have presumably been operating for years and there are several with airlines round the world. So is it reasonable to assume there have been thousands of flights by this aircraft with these engines? Say, being conservative, 1000 flights?
And yet there have been only 2 events (Delta and BA)? So there is 0.002 probability of an event in any particular journey.
I wouldn't worry about odds of that nature.


It's in the US interests to play it up - they want to boost their local (GE) engines and discredit the RR ones.


PS Recently came back from holiday long haul in a BA 777 - I think it had the RR logo on the engines.

[OwlHoot]

Maybe what they need is to incorporate some kind of vibrating mechanism to keep shaking off the ice before it has a chance to build up. Either a lightweight ultrasonic gadget, or even a programmed adjustment to the air or fuel intake to run the engines a bit "juddery" for a few seconds if that makes sense and wouldn't strain anything too much (besides the ice).

Heck, I'm wasted in IT - I should be an aircraft designer

[scooterscot]

So what's needed is a heater for fuel prior to use to make sure optimum temperature is achieved. A small reservoir will also be required I guess for sudden fuel consumption, i.e. landing.

Hard to believe something like this does not already exist, FMEA would have shown this.

[centurian]

The reason it was happening at all was because of the flight procedures being used. The engines were being run at flight minimum during decent - Idling to you and me.

777 is a plane where it is quite difficult to lose altitude quickly - a good thing as it gives it a huge range if both engines fail.

As you say, you need to throttle back to idle just to get from 36,000 ft down to 3,000 in a reasonable timeframe. Even just a bit of thrust will mean the bird will stubornly refuse to descend quickly enough.

But once flaps and landing gear are down on final approach - then you need some thrust to keep the plane in the air - just when all the ice has built up...

[DaveB]

The reason it was happening at all was because of the flight procedures being used. The engines were being run at flight minimum during decent - Idling to you and me. This is done to conserve fuel, and therefore money. With the engines at idle speeds there is not as much heat in the oil/fuel heat exchanger to keep the fuel above freezing point. This is the part that is being redesigned to make it more efficient at lower oil temperatures.

In the mean time flight procedures have bee changed to periodically run the engines at higher thrust to maintain the temperatures needed for the fuel to be kept warmer.

The are also introducing a new procedure to pump fuel between tanks when a temperature difference is indicated to mix the fuel and maintain a higher temperature.

[centurian]

The problem only occurs as the plane approached the runway not at altitude - why is that?

I would expect a blockage to be less of a problem in a warmer climate.

It can happen at altitude as well. It's happened on at least two occasions. Once on final approach (Heathrow) and another at altitude over the US.

The main difference is that when it happens at altitude, the blockage can be cleared quickly by going to max throttle and melting the ice - flight BA38 stalled before the ice melted.

[scooterscot]

"Boeing 777 - it's quite safe as long as you are flying to somewhere warm "

At 30,000 feet it's going to be -50c no mater where you are in the world, the problem came about when the plane descended and the ice thawed leaving small chunks floating about in the fuel lines, this could be just a freak accident but it could potentially happen anywhere.

In fact you could argue that it would be a bigger problem in a warmer area as the thaw could happen at a greater altitude.

The problem only occurs as the plane approached the runway not at altitude - why is that?

I would expect a blockage to be less of a problem in a warmer climate.

[gingerjedi]

"Boeing 777 - it's quite safe as long as you are flying to somewhere warm "

At 30,000 feet it's going to be -50c no mater where you are in the world, the problem came about when the plane descended and the ice thawed leaving small chunks floating about in the fuel lines, this could be just a freak accident but it could potentially happen anywhere.

In fact you could argue that it would be a bigger problem in a warmer area as the thaw could happen at a greater altitude.