Altitude deviation altitude excursion during detour of enroute WX and thunderstorm activity.

Attributes
ACN	179800
Time
Date	199105
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : psk
State Reference	VA
Altitude	msl bound lower : 34800 msl bound upper : 35000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 200 flight time total : 8200 flight time type : 300
ASRS Report	179800
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 24000 flight time type : 10400
ASRS Report	180006
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : published procedure other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : exited adverse environment
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft on autoplt leveled off at FL350 in perf mode. Airspeed bug was approximately 255 KTS or .76 mach. Airspeed was noted at 232 KTS indicated approximately 5 mins later, while deviating east of course for WX to the west. Applied climb power and asked for descent to FL310 to regain speed. Speed continued to decrease to 220 KTS. Center said, 'stand by,' to our request for FL310. However, speed continued to decrease with GA power, so we told center we were now descending to FL310. He said to turn right to 270 degrees and descend to FL310, which we did. We were approximately 34800' when he said to descend to FL310. Center told us there was no traffic conflict. The captain hand-flew the aircraft to FL310 at normal speed and all was then normal. We selected perf cruise later in flight and after approximately 15 mins it disconnected to manual mode by itself. We wrote the pms up at the overnight station.

Original NASA ASRS Text

Title: ALT DEVIATION ALT EXCURSION DURING DETOUR OF ENROUTE WX AND TSTM ACTIVITY.

Narrative: ACFT ON AUTOPLT LEVELED OFF AT FL350 IN PERF MODE. AIRSPD BUG WAS APPROX 255 KTS OR .76 MACH. AIRSPD WAS NOTED AT 232 KTS INDICATED APPROX 5 MINS LATER, WHILE DEVIATING E OF COURSE FOR WX TO THE W. APPLIED CLB PWR AND ASKED FOR DSNT TO FL310 TO REGAIN SPD. SPD CONTINUED TO DECREASE TO 220 KTS. CENTER SAID, 'STAND BY,' TO OUR REQUEST FOR FL310. HOWEVER, SPD CONTINUED TO DECREASE WITH GA PWR, SO WE TOLD CENTER WE WERE NOW DSNDING TO FL310. HE SAID TO TURN RIGHT TO 270 DEGS AND DSND TO FL310, WHICH WE DID. WE WERE APPROX 34800' WHEN HE SAID TO DSND TO FL310. CENTER TOLD US THERE WAS NO TFC CONFLICT. THE CAPT HAND-FLEW THE ACFT TO FL310 AT NORMAL SPD AND ALL WAS THEN NORMAL. WE SELECTED PERF CRUISE LATER IN FLT AND AFTER APPROX 15 MINS IT DISCONNECTED TO MANUAL MODE BY ITSELF. WE WROTE THE PMS UP AT THE OVERNIGHT STATION.

Data retrieved from NASA's ASRS site as of July 2007 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.