Date: 01 Feb 99 02:37:07 From: "P. Wezeman" <email@example.com> Organization: The University of Iowa References: 1 2 3 4 Followups: 1 2
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On 17 Jan 1999, andyweir wrote: > > Considering this happened in the middle of the night during a > >departure out towards the sea, the crew did a pretty good job. They flew > >the airplane for a considerable time and were on their way back to the > >airport when they fell into the trap of believing the altitude the air > >traffic controller gave them. Of course this was just the altitude as > >reported by their transponder, which was also affected by the erroneous > >static pressure. > > Absolutely. But read the CVR transcript for tragedy that affects us all. > You can see them gradually deducing what is wrong, realising that they have > no airspeed, altimeter, etc, etc. that they need help, that this and that > need to be done. But what makes that crash truly scary was that despite all > that, despite knowing the data and instruments were all up the Swanee, they > persistently kept trying to use the autopilot. > > Everyone has safely put the cause down to the taping over the static ports > and one of the men responsible was convicted of negligent homicide. Fair > enough, but there were 27 minutes between declaring the emergency and the > impact with the water. I don't know enough to blame the pilots or not for > not knowing what data was supplied by the air data computer and what was > not, but if pilots are so conditioned to use the autopilot they cannot > abandon it and fly manually even in a screaming emergency, then we could > all be in big trouble. People perform as they train. This would not be the first time common training practices contributed to accidents. Following the Air Florida crash into the Potomic and several other accidents where crew failed to increase power when they should have, it was realised that pilots were always taught to make slow power adjustments and had no quick, automatic "slam it to the firewall" response to a need for more power. The training was changed, though I don't know of any close calls averted by the new training yet. If people have to practice when to fly manually this can be done as well. Didn't Airbus do something recently to make it easier for pilots to disengage their autopilots? Another point: as far as I know, the angle of attack indicator was usable on the airliner with the plugged static ports. I have heard that Navy pilots (they prefer to be called aviators) are taught to use angle of attack as the primary reference when landing. As long as the AOA is correct, the plane cannot stall, whatever the weight or airspeed. The AOA indicator, the visual glide slope, and the angled carrier deck are said to be the three inventions that made it practical to land jets on carriers, and they say it works just as well on land. Clearly, the AOA wouldn't have given the 757 the proper takeoff airspeed, but once they were in the air, AOA plus pitch attitude from the artificial horizon would let them fly level, climb, and descend safely. If there were some greater danger in using AOA I think military experience would have revealed it by now. How often does a pilot follow a malfunctioning AOA into a stall? Peter Wezeman, anti-social Darwinist "Carpe Cyprinidae"