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The mysterious DC9/MD80/717 standby compass

In most commercial aircraft, the standby compass is located on the aircrafts centerline below the over head panel. In some cases, such as the A320 family, the compass can be hidden and hard to find as it can be stowed to be out of the way and out of sight since it is rarely used. But in no aircraft is it harder to find than on the DC-9, MD80 and 717 aircraft series. Although the same case on many other Douglas jet aircraft, in today’s video we will be using the Boeing 717 as an example. ( More...

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CK N 5
The chief purpose at the outfit I still fly for was if both mirrors were placed in the up position (intentionally, by a pilot) it indicated the mechanics had the logbook, we were waiting for an amendment, needed paperwork, etc... but just a reminder all the checklists were on hold, and for whatever reason(s) something was amiss, and we weren't legal to continue.

If the second pilot showed up and saw the mirrors up, the first question was "what are we missing?"

Overall, the DC-9 was a lot like Army Basic Training. I'm grateful for the experience, but would not want to do it again.
Terry Briggs 3
Think they got the mirror trick from the Ryan NYP Spirit of St. Louis?
jaymeinen 4
I am glad that I never had to fly headings using this compass. Surprisingly, the visibility of the compass was better than I expected.
Dennis Simo 4
Used to work on those old birds and it was always fun to send the new kid to the cockpit to clean the compass and wait an hour until he admitted he couldn’t find it. Video is not 100% correct though…the compass does not use small magnets to follow the earths magnetic field. It has small ‘trimming’ magnets to adjust it for deviations but the card (float) itself is highly ferrous and follows the earth’s magnetic field. The earth is the the big magnet.
Bob Myers 1
The card (float) IS the small magnet that aligns with the Earth's field. Just being made of a ferrous material is not enough.
kenish 2
Just my speculation, but I'm not sure this compass setup would meet today's aircraft certification requirements. The compass will be difficult or impossible to read if the compass illumination fails or the cockpit is filled with smoke.
Bandrunner 1
My thought on it, exactly. What happens when the power to the light, or the bulb itself fails.
Russell Hill 2
I spent +/- 9000 hours in the DC9 front office. Both seats. The only reason I left the airplane was that I was too comfortable in it. I needed to be in a cockpit where I was not as comfortable. Pilot training emphasized use of the magnetic compass. Never had to use it, (good maintenance!) though I knew I could if needed (good training!). My experience also includes DC-6, 727, 757, 747., as well as Citations. I will confidently make the statement that most aircraft accidents result from pilot mismanagement or shoddy maintenance.
I always carried a water filled stump and a paper clip when I flew.
Nolan Clinard 1
You really lived your life on The Edge. Hope you didn't forget to bring a leaf.
sparkie624 2
It is a very interesting system, and not a Mechanics dream when it comes to doing a Compass Swing! :)
Ichiro Sugioka 1
Interesting! Who knew besides the pilots?
Howard Hinsdale 1
How does it work when the cockpit fills with smoke from the failed nav equipment?
brownbearwolf 1
Yes the first time I had a ride in the -9's office, I asked where is the compass? Told it doesn't have one but the look on my face was clear I didn't believe the FO. I was shown the mirror that reveled the display hidden in the bulkhead behind the crew seats. Be a hard job swing those compasses.
William Diaz 1
Nice, informative video by MT aviation. It's good to see Samaritan's Purse DC8 in the video. This beautifully maintained airplane was on display on Boeing Plaza a couple of years ago during AirVenture.
ron turnbull 1
Back when I was flying the DC9, we used to use these for shaving in the cockpit.
Rex Bentley 0
The simpelest most reliable piece of equipment on the aiplane and they gotta go rube goldberg it. So much for aviators being smart.
Gary Bain 3
Aviators didn't design it, engineers did.
David Beattie 2
Yes they did! There is a narrow center windscreen section in the DC-9 and MD-80 and the magnetic compass would further restrict the field of vision. That is why the engineers moved the compass. I never heard of a crew actually having to use the magnetic compass. At that point, you would have to be in really big trouble. The fact is the magnetic compass is only accurate when you are in steady level flight. In turns, it has some pretty serious errors built in. If you were down to nothing but a mag compass, ATC would give you a “No gyros” approach issuing you timed turns, NOT mag compass headings.

When we had visitors to the cockpit we would show them “it’s all done with mirrors!”
Michael Ragsdale 1
David, you hit all the highlights with your post. 20,000 hours on the DC-9/MD-80 and I never HAD to use the stand-by compass ... thankfully.
John Taylor 0
Having been a Boeing KC-135 guy my whole life, I hold a grudge against the McDonell-Douglas suits that started using the Boeing designation of 717 for their updated DC-9's. That number has belonged to the 135 since 1955.


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