All three MD80 gyros failed in cruise flight resulting in the loss of autothrottle; Flight Directors and other items. An emergency was declared and the flight diverted to a nearby airport but the failed equipment restored before landing.
Synopsis
All three MD80 gyros failed in cruise flight resulting in the loss of autothrottle; Flight Directors and other items. An emergency was declared and the flight diverted to a nearby airport but the failed equipment restored before landing.
Narrative
I was PM. First indication of problem came at around 10000' MSL when the Autothrottle disconnected along with my (Captain's) FD steering bars biasing out of view and all four FMA windows on my side blanking out. Note- there was NO FD FAIL or any other warning indication displayed and all circuit breakers were in. I ran the Left FD FAIL checklist from the QRH as this was the closest to the problem at hand. When I selected FD CMD BOTH ON 2; I got back the steering bars and FMAs. Completing the checklist; we eventually leveled off. I was a bit concerned that no warning flags illuminated; so I contacted maintenance through Dispatch and discussed the problem. They agreed with my assessment of the situation and intention to continue to the filed destination as there was no 'land at nearest airport' in the procedure I ran. About 45 minutes later; things got weird. This time; BOTH Captain's and First Officer's steering bars disappeared; autopilot and autothrottle disengaged; both sets of FMAs went blank and still NO warning or failure indications anywhere in the cockpit. This is where I declared an emergency and diverted to a nearby airport. I advised the flight attendants of the situation; informed the passengers via PA and sent a diversion report on the ACARS. The First Officer did an outstanding job in hand flying out of 35000' and on toward our divert airport. At about 10000' I assumed the controls for the landing; not really sure what to expect; when all the failed equipment came back to life. We then landed Rwy 12R. Everything worked normally all the way to the gate. When Maintenance ran a test; they told me three of the vertical gyros had failed for a time; which would explain the loss of so many items. Still; why no warning that this had happened? This incident was definitely a first for me in almost twenty years of flying the MD-80. Fortunately; my selection of this particular airport enabled us to get a replacement aircraft and were able to safely get our passengers to their destination about an hour later than scheduled.
NASA callback
The Reporter clarified that this aircraft does not have IRU's; but a standard compass system with wingtip flux valves. He has not gone back into the aircraft's maintenance history since this event and so is relying on the Mechanic's original assessment that all the compass systems failed. He is still puzzled that no alert; warning or other cockpit indication was given about the nature of the failures they experienced. He has been a Captain on the aircraft eight years and First Officer on it four years before that so he have seen many anomalies with it; and for certain this is the strangest. In the end he would put the event in the aging aircraft category.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.