IRU stablized compass

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7 months 1 week ago #1267 by dynamics
As per MMEL rev.62 I have just emailed would you agree with me that INS stablized compass comprised of closed loop control system that direction of IRU gyro is corrected by error signal as a result of difference of heading from flux gate and gyros? Furthermore would you mind advising me if you have seen such a system in boeing models? How ATC radar may replace failed standby compass?

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7 months 1 week ago #1268 by Mark
Replied by Mark on topic IRU stablized compass
You're asking what is needed to continue flight with a inoperative Standby Compass?

To be blunt..... if an aircraft is relying on the Stby Compass for operation, the crew has a lot more on their mind than just aircraft heading. We would be talking a complete electrical system failure (along with loosing the IRS battery feeding the #1 IRS). Chances of that happening..... slim to none.

But..... we're talking M.E.L. requirements here.

The 737-300 and above use three (laser-ringed) Inertial Reference Units. These are stand-alone units. They require no external inputs to function. All they need is to be told what the current position is upon power-up.

Older 737's (-200 and -100), the 727, DC-9, DC-8, and some MD-80's used a Flux Valve (magnetic sensing device near the wing tips) along with a mechanical spinning iron directional gyro. Every aircraft of those types only had two compass systems.

I have never seen an aircraft (nor will I) with both iron gyro's and IRU's. 

Are you still flying -200's? If not, throw the gyro requirement out of that M.E.L.

As far as "positive control of ATC". I guess as long as ATC's used the old spinning ground radar, you could fly with traffic controllers monitoring your position..... but again, that's pretty far-fetched.

Pretty much the majority of flight environment data comes from the IRU's and Air Data Computers. A "minimum" of two each should be required for safe flight.
 

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