False GPWS warning leads to altitude deviation for air carrier flight crew at sea.

Attributes
ACN	176881
Time
Date	199104
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : sea
State Reference	WA
Altitude	msl bound lower : 5000 msl bound upper : 7000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : sea
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	landing : missed approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : commercial pilot : cfi pilot : atp pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 10500 flight time type : 300
ASRS Report	176881
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 32 flight time total : 3992 flight time type : 32
ASRS Report	176768
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	Pilot Deviation

Narrative:

During an ILS approach to runway 16R at sea, the runway closed due to people on runway and we were instructed to discontinue approach and climb to 5000' MSL on runway heading. Upon leveling at 5000' MSL, the GPWS issued a 'terrain, terrain' warning. We began an immediate climb and asked for clearance for 7000'. We were cleared to 7000' as requested, but were told that in our location it was flat terrain and no conflict should exist. Upon landing at pdx, maintenance performed required test and found no fault existed. Recent history of aircraft found false G/south warning on GPWS while in cruise. At that time the GPWS computer was changed by maintenance.

Original NASA ASRS Text

Title: FALSE GPWS WARNING LEADS TO ALT DEVIATION FOR ACR FLT CREW AT SEA.

Narrative: DURING AN ILS APCH TO RWY 16R AT SEA, THE RWY CLOSED DUE TO PEOPLE ON RWY AND WE WERE INSTRUCTED TO DISCONTINUE APCH AND CLB TO 5000' MSL ON RWY HDG. UPON LEVELING AT 5000' MSL, THE GPWS ISSUED A 'TERRAIN, TERRAIN' WARNING. WE BEGAN AN IMMEDIATE CLB AND ASKED FOR CLRNC FOR 7000'. WE WERE CLRED TO 7000' AS REQUESTED, BUT WERE TOLD THAT IN OUR LOCATION IT WAS FLAT TERRAIN AND NO CONFLICT SHOULD EXIST. UPON LNDG AT PDX, MAINT PERFORMED REQUIRED TEST AND FOUND NO FAULT EXISTED. RECENT HISTORY OF ACFT FOUND FALSE G/S WARNING ON GPWS WHILE IN CRUISE. AT THAT TIME THE GPWS COMPUTER WAS CHANGED BY MAINT.

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.