Jan 28, 2008

Fuel Slushies?

The investigation into British Airway's B-777 landing-short accident is apparently now concentrating on fuel. This article indicates fuel contamination is high on the list of suspects. Also:

" ... Sources also tell The DAILY that upper air temperatures over Russia and northern Europe were extremely cold on the day of the accident. Information from other crews coming from Asia on Jan. 17 encountered extremely low temperatures in the -70 to -75 degrees C. range, resulting in fuel temperatures dipping into the -40s. European upper air temperatures also indicate the last 6.5 hours of the inbound China flight would have been flown at an outside air temperature of -60 deg. C. or lower. Although this would have resulted in fuel temperatures on approach in the -35 degrees C range, this would not normally constitute a problem unless, potentially, contaminants were present."

The fact that the fuel temps were close to the minimum allowable range is interesting. Jet A fuel has an "official" freezing point of -43 degrees C., but the minimum allowable temperature of the fuel in the tank on the A320 aircraft (for comparison) is limited to -36C. This has to do with viscosity changes and "slushiness" that can occur causing cavitaition problems for fuel "boost" pumps inside the tanks.

Some aircraft have used strategies to circulate cold fuel (in wing tip tanks) with warmer fuel (for example, in body tanks) to allow for extended flight time in very cold conditions. I don't know if the B-777 does this.

Prior to fuel reaching the engine, it passes through a filter. A significant drop of pressure across the filter is interpreted as ice crystals forming, at which point a fuel heating system will kick in. The Second Officer manually controlled this system on older aircraft such at the B-727. There were cases where engines lost power because the system was inadvertantly left on too long, triggering fuel vaporization in the lines.

Manual fuel heat controls from the B727

I'm sure all these factors and others will be investigated closely to determine if the fuel system operated normally or somehow contributed to the problem.

3 comments:

Anonymous said...

You know what?
I'm a little weary of the public making "Heroes" of this crew. What they did was: kept the wings level and extended the final glide. So what?
What the hell else could they do?
Get out of the seat and go to the bathroom? I think not.

Aviatrix said...

Ah, Anonymous, you have to play the game. The general public thinks that it takes a personal act of heroism to get the airplane in the air in the first place, and want to believe that the pilots have some power to protect the passengers from the random whims of fate and technology.

So when something goes wrong the pilot stays calm and does what training dictates, even if it's going back beyond type training to initial training on a single engine airplane. The pilot then says, "I did what any pilot would have done," and passengers get back on planes.

And in this case the media are only following their own ingrained checklist when a pilot named Coward lands an airplane in an emergency.

Aluwings said...

At this point we don't really know much about what the pilots did or didn't do. But during intial training for the A320, landing with complete loss of flight computers, and so having only the rudder and elevator trim as controls, the exercise was considered successful if we landed "on or in the vicinity of the runway..."

These pilots did that much without stalling the aircraft. Did they have normal instrumentation to accomplish this? Did they lose the airspeed indicators and stall warning systems when the engines spooled down and all the generators went off-line? As I say - we don't know for sure. But the passengers and crew walked away to fly another day.

Now, for another accident, but with much more humour!

If you don't understand French, sorry. You will notice the first officer look suddenly tense when the Captain announces that their only hope of survival is to eat the copilot.

"Why me?" he demands. Well according to regulations it is forbidden to eat passengers, and of course he's much more tender. And nutritious enough to last two weeks if they eat slowly.

Phew! Close call... (hurry, learn French before the next episode!) I love these animations.