Showing posts with label 777 Crash. Show all posts
Showing posts with label 777 Crash. Show all posts

Thursday, July 25, 2013

Asiana 214 crash. The autothrottle did it

The 777 auto throttle has a lot of modes.  Push buttons on the mode control panel are labeled "Auto Throttle", "Vertical Nav" and "Flight Level Change".  Experts on the 777 are saying that the "Flight Level Change" mode actually pulls the throttles back to flight idle and leaves them there.  And they think the Asiana crew somehow selected Flight Level Change instead of "Auto Throttle".  What the Vertical Nav mode might do is unmentioned.  Apparently Flight Level Change is actually a strange kind of standby, I cannot think why a pilot would use the "Flight Level Change".  The situation is so bad that 777 pilots refer to the problem as the "Flight Level Change trap". 
   Sounds like some human factors work wasn't done right when the 777 was designed.  On the other hand, the plane has been flying for 20 years accident free, so it cannot be all wrong.   Certainly the crew failed to monitor airspeed during the landing.  

Wednesday, July 17, 2013

Asiana 214 Has Automation Trumped Airmanship?

Asiana 214,  the 777 that crashed at San Francisco last week, came in too low and too slow, and hit the seawall at the end of the runway.  Apparently the crew had set the autothrottle to hold the proper airspeed (137 knots) and for some reason the autothrottle allowed the airspeed to slack off too much.   The crew didn't notice until it was too late.
    They haven't said if the autothrottle failed, or wasn't set correctly, or for some software reason decided not to hold the setting.  The Aviation Week article goes into some detail about the various modes of the autothrottle, in some modes, it doesn't work the throttles, and it can change modes on its own without notifying the pilot.
   Autothrottle is a new fangled luxury.  Back in my day, only the C141 jet transport had autothrottle, and that was part of the All Weather Landing System, unique to the C141.  All the other aircraft had a plain old throttle lever, the engine power stayed where it was set by hand.  And they all managed to land in one piece.

    Speed on landing approach is critical.  You want to come in as slow as possible.  Slow makes it easier to get the wheels on the runway (as opposed to in the weeds), easier to get the plane stopped before running off the far end of the runway, and  lessens the shock on gear and airframe.  Too much shock breaks things and blows tires.
  On the other hand, go too slow and the wing stalls, stops producing lift, and the aircraft falls like a stone.  All control is lost.  There is little difference between proper landing speed and stall speed.
   It's hard to understand how the crew failed to check their approach speed, and notice that the autothrottle was playing them false.  For that matter it's hard to understand why they used autothrottle at all.  Was it me, with few hours in the 777, I'd  tend to do things by hand, the old fashioned way, rather than find out what nasty bugs might lurk in a tricky newfangled autothrottle.

Saturday, July 6, 2013

Innumeracy at San Francisco

The TV news has been going berserk about the 777 crash in San Francisco today.  They had the San Francisco lady fire chief up in front of the TV.  The question we all want answered, How many people made it off the plane alive?  She didn't answer that question, and none of the newsies were smart enough to ask it. She did say that the airline reported 307 souls on board.  She allowed as how 48 survivors were hospitalized and 192 turned up at the airport.  That's only 240 people.  What happened to the other 67?  Did they fail to get off and burn to death when the plane caught fire? Did they wander off the airport in the confusion and take taxis to where ever they were going?  Are they still wandering around in the tall grass off Runway 28L?  Are they stuck in customs?
   I expected a fire chief to know how to count.  This one clearly didn't.  Probably never did learn the new math. 
   Also kinda disgusting, all the officials called it "an incident".  Here they have a burned out airliner still smoking on the runway, debris all over the runway, and they can't come right out and say "accident"?  What's wrong with this picture?