<< >> NASA ASRS Report 151590, July 1990

Air carrier widebody transport descends below assigned altitude when captain mistakes autoplt disconnect for push to talk switch.

Attributes
ACN	151590
Time
Date	199007
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ilwn airport : dfw
State Reference	TX
Altitude	msl bound lower : 2700 msl bound upper : 3000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dfw
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent : approach
Route In Use	approach : straight in
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 165 flight time total : 11900 flight time type : 800
ASRS Report	151590
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Inbound to the airport, we were kept high to cross the airport for an approach to runway 13R. While descending at a good rate and approaching 3000', with the autoplt on, I reached for the push to talk switch on the yoke to answer a call from approach. I accidentally hit the autoplt release switch. I went through 3000' and began to put back pressure on the yoke. I looked at the altimeter and saw 2700'. I climbed back up to 3000' from that point a successful and landing was made. To prevent an occurrence of this nature from happening again, I will return to my basic philosophy of I will fly the airplane and you will talk on the radio. Another thought, I was on the third day of a three day trip. The first two days was large transport a flying. This happened on the first widebody transport B leg. The back pressure is different on the two aircraft.

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Original NASA ASRS Text

Title: ACR WDB DESCENDS BELOW ASSIGNED ALT WHEN CAPT MISTAKES AUTOPLT DISCONNECT FOR PUSH TO TALK SWITCH.

Narrative: INBND TO THE ARPT, WE WERE KEPT HIGH TO CROSS THE ARPT FOR AN APCH TO RWY 13R. WHILE DSNDING AT A GOOD RATE AND APCHING 3000', WITH THE AUTOPLT ON, I REACHED FOR THE PUSH TO TALK SWITCH ON THE YOKE TO ANSWER A CALL FROM APCH. I ACCIDENTALLY HIT THE AUTOPLT RELEASE SWITCH. I WENT THROUGH 3000' AND BEGAN TO PUT BACK PRESSURE ON THE YOKE. I LOOKED AT THE ALTIMETER AND SAW 2700'. I CLBED BACK UP TO 3000' FROM THAT POINT A SUCCESSFUL AND LNDG WAS MADE. TO PREVENT AN OCCURRENCE OF THIS NATURE FROM HAPPENING AGAIN, I WILL RETURN TO MY BASIC PHILOSOPHY OF I WILL FLY THE AIRPLANE AND YOU WILL TALK ON THE RADIO. ANOTHER THOUGHT, I WAS ON THE THIRD DAY OF A THREE DAY TRIP. THE FIRST TWO DAYS WAS LGT A FLYING. THIS HAPPENED ON THE FIRST WDB B LEG. THE BACK PRESSURE IS DIFFERENT ON THE TWO ACFT.

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.