Altitude deviation when under radar control and GPWS activated.

Attributes
ACN	258519
Time
Date	199312
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ida
State Reference	ID
Altitude	msl bound lower : 11000 msl bound upper : 13000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute airway : v330
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 5100 flight time type : 1500
ASRS Report	258519
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial
Experience	flight time last 90 days : 75 flight time total : 9000
ASRS Report	258514
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action other other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Cruising in IMC on V330, 11000 ft MSL, 35 DME east of ida VOR, we experienced a GPWS 'terrain, terrain' warning, followed by a 'pull up' command. We immediately executed company procedure climb. Terrain warning ceased passing approximately 12100 ft MSL. We leveled at 13000 ft MSL. We advised ZLC of our actions. The controller advised us that we should have 2000 ft of terrain clearance with an altitude of 11000 ft MSL in our location. We descended back to 11000 ft MSL inside of 30 DME to ida VOR. We were experiencing moderate to severe rime airframe icing throughout this episode. Continued descent to landing at ida. Unsure as to why GPWS would have gone off with adequate terrain clearance. Altitude should have been well clear of terrain in that area.

Original NASA ASRS Text

Title: ALTDEV WHEN UNDER RADAR CTL AND GPWS ACTIVATED.

Narrative: CRUISING IN IMC ON V330, 11000 FT MSL, 35 DME E OF IDA VOR, WE EXPERIENCED A GPWS 'TERRAIN, TERRAIN' WARNING, FOLLOWED BY A 'PULL UP' COMMAND. WE IMMEDIATELY EXECUTED COMPANY PROC CLB. TERRAIN WARNING CEASED PASSING APPROX 12100 FT MSL. WE LEVELED AT 13000 FT MSL. WE ADVISED ZLC OF OUR ACTIONS. THE CTLR ADVISED US THAT WE SHOULD HAVE 2000 FT OF TERRAIN CLRNC WITH AN ALT OF 11000 FT MSL IN OUR LOCATION. WE DSNDED BACK TO 11000 FT MSL INSIDE OF 30 DME TO IDA VOR. WE WERE EXPERIENCING MODERATE TO SEVERE RIME AIRFRAME ICING THROUGHOUT THIS EPISODE. CONTINUED DSCNT TO LNDG AT IDA. UNSURE AS TO WHY GPWS WOULD HAVE GONE OFF WITH ADEQUATE TERRAIN CLRNC. ALT SHOULD HAVE BEEN WELL CLR OF TERRAIN IN THAT AREA.

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.