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MDI Compasses On A Martin 404  
User currently offlineTom in NO From United States of America, joined Nov 1999, 7194 posts, RR: 31
Posted (11 years 1 week 2 days 15 hours ago) and read 2071 times:

I'm still doing some research on a Martin 404 crash outside Albuquerque in 1955.

4 compasses are mentioned in the accident report (2 RMI's and 2 MDI's). In looking at a picture of the 404's panel, I see the two RMI's on either side of the panel.

Can someone point out the two MDI's?

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Tom at MSY

"The criminal ineptitude makes you furious"-Bruce Springsteen, after seeing firsthand the damage from Hurricane Katrina
4 replies: All unread, jump to last
User currently offlineCaboclo From United States of America, joined Nov 2004, 203 posts, RR: 0
Reply 1, posted (11 years 1 week 17 hours ago) and read 2017 times:

Just a guess, MDI = magnetic direction indicator, ie a plain whisky compass. One is usually somewhere around the center of the windshield, don't know about the other one.

Freight dogs have more fun
User currently offlineLongHauler From Canada, joined Mar 2004, 6004 posts, RR: 43
Reply 2, posted (11 years 1 week 6 hours ago) and read 2006 times:

If I recall, the RMIs would have the fluxgate compass as their source. The compasses in the cockpit, ie the "whiskey" compasses are a backup.

The old fluxgate compass, with the sensing needle are 3 from the left on the top of the captain's panel. And, another one, 3 from the right on the top of the F/Os panel. Curiously, they are almost 180 degrees apart, one indicating approx 300, the other 150 degrees!

The manual backup compass, is probably above the top of the panel, out of the range of the picture, to keep it clear of interference from the instruments.

You probably know this, but Robert Serling, included a lot of information about Ivon Spong, and that crash is his book, "The Probable Cause". Suspicion about the fluxgate compass system was one of the possible causes of the crash.

Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!
User currently offlineTom in NO From United States of America, joined Nov 1999, 7194 posts, RR: 31
Reply 3, posted (11 years 6 days 16 hours ago) and read 1990 times:


Thanks for the info. What got me back interested was when I recently came across the supplemental CAB accident report. It's the one that changed the probable cause from an "intended" flight path taken by the pilots to one taken for reasons "unknown".
http://dotlibrary1.specialcollection...dll?websearch&site=dot_aircraftacc (won't let me do a direct link)

Not being a pilot myself, yet trying to understand the complexities of instrument operation, I was trying to further my limited cockpit knowledge with a better picture of the location of the various instruments.

"The Probable Cause" is an excellent book, and the place I first heard this crash many years ago. His other books, both non-fiction and fiction, are excellent reads, as well.

Tom at MSY

"The criminal ineptitude makes you furious"-Bruce Springsteen, after seeing firsthand the damage from Hurricane Katrina
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 4, posted (11 years 6 days 7 hours ago) and read 1975 times:

A very similar DC-6 accident, with the compass system as the probable cause, occured on the east coast.
Early Sperry remote compass systems utilized three phase AC current for operation (provided by an inverter...IE: a DC motor driving an AC generator, not a static inverter) and every once in awhile, one of the phases would fail, providing an erroneous compass reading.
While flying the DC-6B, I experienced three such failures, and in each case, the compass (RMI) indicated a 120 degree bearing error.

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