Medium large transport has altitude deviation due to TCASII RA.

Attributes
ACN	257984
Time
Date	199312
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : phl
State Reference	PA
Altitude	msl bound lower : 9500 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : phl tower : bos
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 14000 flight time type : 200
ASRS Report	257984
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 60 flight time total : 10000
ASRS Report	257983
Events
Anomaly	altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 0 vertical : 1000
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

While leveled off at 10000 ft MSL, TCASII TA sounded, followed 15 seconds later by TCASII RA. TCASII RA commanded 2500 FPM descent. Left 10000 ft MSL, stopped descent at 9500 ft MSL, when conflict cleared. Climbed back to 10000 MSL, advised ATC that we left assigned altitude and returned to assigned altitude because of TCASII RA.

Original NASA ASRS Text

Title: MLG HAS ALTDEV DUE TO TCASII RA.

Narrative: WHILE LEVELED OFF AT 10000 FT MSL, TCASII TA SOUNDED, FOLLOWED 15 SECONDS LATER BY TCASII RA. TCASII RA COMMANDED 2500 FPM DSCNT. LEFT 10000 FT MSL, STOPPED DSCNT AT 9500 FT MSL, WHEN CONFLICT CLRED. CLBED BACK TO 10000 MSL, ADVISED ATC THAT WE LEFT ASSIGNED ALT AND RETURNED TO ASSIGNED ALT BECAUSE OF TCASII RA.

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.