Flight crew of an medium large transport air carrier aircraft descended below assigned cruise altitude in response to a TCASII RA. After returning to assigned altitude, the flight crew noticed that they had failed to reset their altimeter to the standard 29 pt 92!

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Attributes
ACN	258629
Time
Date	199312
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : imp
State Reference	CA
Altitude	msl bound lower : 26000 msl bound upper : 27300
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zla
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
Route In Use	enroute airway : zla
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 240 flight time total : 19000 flight time type : 8000
ASRS Report	258629
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 220 flight time total : 15000 flight time type : 220
ASRS Report	258418
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action flight crew : returned to intended course or assigned course other
Consequence	Other
Miss Distance	horizontal : 0 vertical : 700
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Heading eastbound from san diego, ca, to phoenix, az. While cruising at an intermediate cruise level of 270, we were advised by ATC of wbound traffic (an air carrier Y airlines plane) that was descending to FL280. Our TCASII display showed that traffic heading right toward us and descending toward us too. I commented to the first officer that it concerned me and that I might take an evasive maneuver. Just as I switched the autoplt selector from 'command' to 'control wheel steering' the TCASII commanded an 'RA,' 'descend, descend,' and I did. We returned to FL270 upon ending of conflict. We heard ATC advising air carrier Y of a possible altitude deviation on their part. We then noticed that our altimeters were still set to 30.19, instead of 29.92. Could that be a contributing factor to this conflict?

Original NASA ASRS Text

Title: FLC OF AN MLG ACR ACFT DSNDED BELOW ASSIGNED CRUISE ALT IN RESPONSE TO A TCASII RA. AFTER RETURNING TO ASSIGNED ALT, THE FLC NOTICED THAT THEY HAD FAILED TO RESET THEIR ALTIMETER TO THE STANDARD 29 PT 92!

Narrative: HDG EBOUND FROM SAN DIEGO, CA, TO PHOENIX, AZ. WHILE CRUISING AT AN INTERMEDIATE CRUISE LEVEL OF 270, WE WERE ADVISED BY ATC OF WBOUND TFC (AN ACR Y AIRLINES PLANE) THAT WAS DSNDING TO FL280. OUR TCASII DISPLAY SHOWED THAT TFC HDG RIGHT TOWARD US AND DSNDING TOWARD US TOO. I COMMENTED TO THE FO THAT IT CONCERNED ME AND THAT I MIGHT TAKE AN EVASIVE MANEUVER. JUST AS I SWITCHED THE AUTOPLT SELECTOR FROM 'COMMAND' TO 'CTL WHEEL STEERING' THE TCASII COMMANDED AN 'RA,' 'DSND, DSND,' AND I DID. WE RETURNED TO FL270 UPON ENDING OF CONFLICT. WE HEARD ATC ADVISING ACR Y OF A POSSIBLE ALTDEV ON THEIR PART. WE THEN NOTICED THAT OUR ALTIMETERS WERE STILL SET TO 30.19, INSTEAD OF 29.92. COULD THAT BE A CONTRIBUTING FACTOR TO THIS CONFLICT?

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.