B737-500 flight crew loses both autoplts in rvsm airspace.

Attributes
ACN	794280
Time
Date	200807
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 37000
Environment
Flight Conditions	VMC
Aircraft 1
Controlling Facilities	artcc : zzz.artcc tower : lfpg.tower
Operator	common carrier : air carrier
Make Model Name	B737-500
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 240 flight time total : 10500 flight time type : 6000
ASRS Report	794280
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted other
Supplementary
Problem Areas	Aircraft Airspace Structure
Primary Problem	Aircraft

Narrative:

Experienced a dual autoplt failure. We were at FL370 with autoplt B engaged in LNAV and VNAV. The first officer left the cockpit to use the restroom. The autoplt disconnect horn sounded so I took manual control of the aircraft and pushed the B autoplt button in an attempt to get the autoplt back on line. The B autoplt would not reengage. I was hand flying the aircraft and reached over and pushed the a autoplt button; the a autoplt would not engage either. The first officer returned and I continued flying the aircraft. I directed the first officer to attempt to reengage the autoplts after cycling the master autoplt disconnect switch. Neither autoplt would engage. I then had the first officer call dispatch and get a phone patch to maintenance control to troubleshoot the problem. I was flying the aircraft and working the radios with ATC. I informed ATC of our situation as we were in rvsm airspace with no autoplt. The first officer with direction from maintenance control cycled the circuit breakers for both autoplts with no luck. I informed ATC that we were unable rvsm and they had us descend to FL270.

Original NASA ASRS Text

Title: B737-500 FLT CREW LOSES BOTH AUTOPLTS IN RVSM AIRSPACE.

Narrative: EXPERIENCED A DUAL AUTOPLT FAILURE. WE WERE AT FL370 WITH AUTOPLT B ENGAGED IN LNAV AND VNAV. THE FO LEFT THE COCKPIT TO USE THE RESTROOM. THE AUTOPLT DISCONNECT HORN SOUNDED SO I TOOK MANUAL CTL OF THE ACFT AND PUSHED THE B AUTOPLT BUTTON IN AN ATTEMPT TO GET THE AUTOPLT BACK ON LINE. THE B AUTOPLT WOULD NOT REENGAGE. I WAS HAND FLYING THE ACFT AND REACHED OVER AND PUSHED THE A AUTOPLT BUTTON; THE A AUTOPLT WOULD NOT ENGAGE EITHER. THE FO RETURNED AND I CONTINUED FLYING THE ACFT. I DIRECTED THE FO TO ATTEMPT TO REENGAGE THE AUTOPLTS AFTER CYCLING THE MASTER AUTOPLT DISCONNECT SWITCH. NEITHER AUTOPLT WOULD ENGAGE. I THEN HAD THE FO CALL DISPATCH AND GET A PHONE PATCH TO MAINT CTL TO TROUBLESHOOT THE PROB. I WAS FLYING THE ACFT AND WORKING THE RADIOS WITH ATC. I INFORMED ATC OF OUR SITUATION AS WE WERE IN RVSM AIRSPACE WITH NO AUTOPLT. THE FO WITH DIRECTION FROM MAINT CTL CYCLED THE CIRCUIT BREAKERS FOR BOTH AUTOPLTS WITH NO LUCK. I INFORMED ATC THAT WE WERE UNABLE RVSM AND THEY HAD US DSND TO FL270.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.