Altitude deviation altitude overshot in descent.

Attributes
ACN	204400
Time
Date	199203
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : har
State Reference	PA
Altitude	msl bound lower : 16700 msl bound upper : 17000
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Controlling Facilities	artcc : zny tower : zzz
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : instrument pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 165 flight time total : 18000 flight time type : 4680
ASRS Report	204400
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 700
ASRS Report	204331
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other controllera 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:

We were cleared from FL190 to 17000 ft. We descended through 17000 to 16700 ft when the aircraft leveled and started back up to 17000 ft. At that same time we had an altitude alert, a TCASII TA and a call from center asking our altitude. We reported 16900 to level at 17000. The TCASII indicated a contact 800 ft low, 8 mi and at 10 O'clock. We were back at 17000 when the traffic at 16000 passed about 5 mi behind us. The only thing that I can attribute this to is when I changed the altimeters to 29.54 from 29.92 it wasn't quick enough. I'm sure I was making the change as we were going through FL180. When cleared to an altitude only 1000 ft below the transition altitude you have to be very alert to this potential problem. Supplemental information from acn 204331: there was no conflict and there was no RA. It is possible the #3 altimeter was reset after the FMC was within the capture mode (approximately 1000 ft) of level off altitude and computed level off at 17000 with 29.92 instead of 29.59 that was put in at FL180. I now believe it would be better to set the altimeter first then set the altitude and initiate automatic descent second.

Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT IN DSCNT.

Narrative: WE WERE CLRED FROM FL190 TO 17000 FT. WE DSNDED THROUGH 17000 TO 16700 FT WHEN THE ACFT LEVELED AND STARTED BACK UP TO 17000 FT. AT THAT SAME TIME WE HAD AN ALT ALERT, A TCASII TA AND A CALL FROM CTR ASKING OUR ALT. WE RPTED 16900 TO LEVEL AT 17000. THE TCASII INDICATED A CONTACT 800 FT LOW, 8 MI AND AT 10 O'CLOCK. WE WERE BACK AT 17000 WHEN THE TFC AT 16000 PASSED ABOUT 5 MI BEHIND US. THE ONLY THING THAT I CAN ATTRIBUTE THIS TO IS WHEN I CHANGED THE ALTIMETERS TO 29.54 FROM 29.92 IT WASN'T QUICK ENOUGH. I'M SURE I WAS MAKING THE CHANGE AS WE WERE GOING THROUGH FL180. WHEN CLRED TO AN ALT ONLY 1000 FT BELOW THE TRANSITION ALT YOU HAVE TO BE VERY ALERT TO THIS POTENTIAL PROBLEM. SUPPLEMENTAL INFO FROM ACN 204331: THERE WAS NO CONFLICT AND THERE WAS NO RA. IT IS POSSIBLE THE #3 ALTIMETER WAS RESET AFTER THE FMC WAS WITHIN THE CAPTURE MODE (APPROX 1000 FT) OF LEVEL OFF ALT AND COMPUTED LEVEL OFF AT 17000 WITH 29.92 INSTEAD OF 29.59 THAT WAS PUT IN AT FL180. I NOW BELIEVE IT WOULD BE BETTER TO SET THE ALTIMETER FIRST THEN SET THE ALT AND INITIATE AUTO DSCNT SECOND.

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.