|Quoting Ex52tech (Reply 63):|
Quoting PGNCS (Reply 62):
I understand it was perpetuated into the DC-10 program, but I can't verify that personally.
I'm not sure if you mean the problems followed along into the DC-10 program, but it's mag compass was mounted right out in front, plain sight. Well you could flip it up out of your way if you wanted to. Swung quite a few compasses on DC-10s, I don't recall hearing about any accuracy problems from structural or electronic interference.
Thanks, Ex52tech, I stand corrected. I had been told that the DC-10 compass was mounted similarly, but that is obviously bad information. That's why I made the disclaimer that I couldn't personally verify that information. Thanks for the info!
I am not, by the way, claiming there is any significant interference with the compass on the DC-9/MD-80 fleet there; I am claiming that that is what the guys I talked to at Douglas when I was heavily involved with the DC-9 program claimed. For further third party information that I can't verify (if anyone can clarify, please join in) there was evidently a difference between power on and off in the annuniciator panel that amounted to a slight (but practically negligible) difference in compass readings. Evidently the FAA down in Long Beach interpreted certification regulations differently than everyone else and wouldn't allow the compass there which is where I'm told it was originally conceived to be, and where it is on pretty much every other airliner brand of I have ever flown. Like I said, this seems remotely plausible to me, but I don't have specifics as this story was related by Douglas staff to me several times either in person or over the phone. The Douglas guys totally blamed the FAA for an implausible interpretation of regs forcing them do something seemingly ridiculous. If in fact that is a true story, I would personally like to meet the FAA genius who thought this was a better idea, as I have actually had to fly the airplane with the thing, and it is far more difficult than you can imagine if you haven't done it yourself. It's my single least favorite piece of engineering in the aircraft.
|Quoting HAWK21M (Reply 64):|
Quoting PGNCS (Reply 62):
The Douglas guys I spoke with back in the DC-9 era said it was due to issues with the proximity to the annunciator panel and its impact on accuracy of the standby compass.
Whats in the annunciator panel thats contributing to the magnetic drift?
According to the people at Douglas I spoke with it was an issue of slightly variable compass readings depending on whether power was on or off to the annunciator panel, and because it was felt that depending on what combination of annunciator lights were on or off that the compass accuracy could be degraded. I honestly have no idea if that is true or not (see above), but I relate the story from the most authoritative source I know of. If any engineers from Douglas know the real story, please let us know, because this is a very odd piece of engineering and those of us with an interest in the aircraft would love to know the whole truth.