could it be that illegal substandard parts might be involved in latest MD series accident and snafus?greenspun.com : LUSENET : TimeBomb 2000 (Y2000) : One Thread
---I have seen several expose' type reports on the tube where companies that supply parts to the airplane industry have been caught selling alledgedly "certified" parts that in reality were not. Could the alaskan airlines company be a victim of purchasing and installing just a batch of similar wrong parts? It might be an explanation for what has been happening. If the problems persist, it would be something to look at. Are there new parts companies that the airliner company recently switched to, or maybe their normal "suppliers" have gone to someplace else to save some money, and been burned with bad parts?
-- worthconsidering (email@example.com), February 08, 2000
There is an uncanny similarity between the Alaska Airlines accident and the scenario in Michael Chriton's novel, "Airframe".
Part of the problem there was "counterfeit" parts, and it was exacerbated by other things; I won't tell you, as I don't want to spoil the suspense, but computers play a part.
All you paranoids, and I'm sure you know who you are (NOT), should definitely read this book. It will give you a topic to freak out about for weeks!
-- jumpoff joe a.k.a. Al K. Lloyd (firstname.lastname@example.org), February 08, 2000.
Made in China? There was a link here a few days ago, I think, but don't remember title or topic. Anyway. A lot of parts coming from China are fraudulently certified. But I don't know if any such are on MD-80 tails, though.
What was interesting to me is that tail problems on other planes after the crash were SUPPOSEDLY cause by pilots running a more extensive preflight test, causing overheating of servo motors or whatever and resultant problems. If that is so, that running for a minute and a half or two vs. one minute can cause a problem -- THAT IS A DESIGN SAFETY DEFECT.
-- A (A@AisA.com), February 08, 2000.
The problem of overheated motors on the ground is not an airborne problem. The motors are cooled by airflow and there isn't any when the plane is sitting at the gate or on the taxiway while the pilot and co-pilot take turns running the pitch trim from neutral to full nose up, to full nose down and back to neutral again.
Manually running the trim from limit to limit is something you normally do once for each axis during ground checks on older aircraft. On newer birds you push the "Pre-Flight BIT" (Built In Test) button and the computer checks itself and all the flight control system.
But either way, the check is only supposed to be done once, unless there is a malfunction found during the check. Running additional check is counter productive beyond that point.
-- Wildweasel (email@example.com), February 08, 2000.
WW: Theoretically, anyway. I assume you're saying that while in flight, they only need to goose the controls occasionally and that they will cool by airflow between gooses. What happens if they need to continually adjust? (As in an emergency situation?) Enough cooling then?
-- A (A@AisA.com), February 09, 2000.
Inflight, certainly yes. The outside air temps drop off to minus forty and colder pretty quick as you get higher in altitude. The motor probably has a constant operation rating of fifteem minutes or more under those conditions.
Meanwhile on the ground, the tail section of a DC-9/MD-80 could get pretty warm. The engines are back there as is the APU (auxiliary power unit) if I'm not mistaken. With everything running it could easily get up over one hundred degrees air temp within the tail structure, even on a cool day outside.
Run a trim motor constantly at that temp and you could probably cook the thing in three minutes. That's why there's a thermal protection device connected to the motors which shuts off the power after they've heated up to around 90 seconds worth of operation.
And when the motor quits running because it's gone into overheat, the crew reports it as a trim problem, not realizing that they've caused it themselves.
-- Wildweasel (firstname.lastname@example.org), February 09, 2000.