<< >> NASA ASRS Report 250975, September 1993

Pilot of an small transport jet government aircraft inadvertently overshot descent altitude assignment.

Attributes
ACN	250975
Time
Date	199309
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : mgm
State Reference	AL
Altitude	msl bound lower : 21500 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx tower : den
Operator	other
Make Model Name	Small Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	government other
Function	flight crew : single pilot
Qualification	pilot : instrument
Experience	flight time last 90 days : 40 flight time total : 4200 flight time type : 2000
ASRS Report	250975
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was directed by ATC to descend from my assigned altitude of FL390 to FL240. Later I was directed to descend so as to reach FL240 within 4 mins. I did a quick calculation from the altitude I was passing and concluded I needed at least 4000 FPM. After about 1 min I assumed I had 12000 ft left to descend and realized this would put me at FL200. At this time I incorrectly assumed I was cleared to descend to FL200 even though I had entered FL240 in an altitude memory counter earlier. I became preoccupied with meeting the FL200 restr and didn't realize the error until passing about 21500 ft. At this point the ATC controller caught the error and directed that I maintain FL210. I believe that a preoccupation with converting altitude to lose to FPM resulted in this error. Most of my descent restrs in the past were based on distance rather than time.

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Original NASA ASRS Text

Title: PLT OF AN SMT JET GOV ACFT INADVERTENTLY OVERSHOT DSCNT ALT ASSIGNMENT.

Narrative: I WAS DIRECTED BY ATC TO DSND FROM MY ASSIGNED ALT OF FL390 TO FL240. LATER I WAS DIRECTED TO DSND SO AS TO REACH FL240 WITHIN 4 MINS. I DID A QUICK CALCULATION FROM THE ALT I WAS PASSING AND CONCLUDED I NEEDED AT LEAST 4000 FPM. AFTER ABOUT 1 MIN I ASSUMED I HAD 12000 FT LEFT TO DSND AND REALIZED THIS WOULD PUT ME AT FL200. AT THIS TIME I INCORRECTLY ASSUMED I WAS CLRED TO DSND TO FL200 EVEN THOUGH I HAD ENTERED FL240 IN AN ALT MEMORY COUNTER EARLIER. I BECAME PREOCCUPIED WITH MEETING THE FL200 RESTR AND DIDN'T REALIZE THE ERROR UNTIL PASSING ABOUT 21500 FT. AT THIS POINT THE ATC CTLR CAUGHT THE ERROR AND DIRECTED THAT I MAINTAIN FL210. I BELIEVE THAT A PREOCCUPATION WITH CONVERTING ALT TO LOSE TO FPM RESULTED IN THIS ERROR. MOST OF MY DSCNT RESTRS IN THE PAST WERE BASED ON DISTANCE RATHER THAN TIME.

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.