<< >> NASA ASRS Report 484080, August 2000

A DHC8 flight crew experienced a false warning from their GPWS and failed to note the anomaly in their logbook after flight termination at pdx, or.

Attributes
ACN	484080
Time
Date	200008
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : pdx.vortac
State Reference	OR
Altitude	msl bound lower : 1800 msl bound upper : 2500
Environment
Flight Conditions	IMC
Light	Dawn
Aircraft 1
Controlling Facilities	tracon : p80.tracon
Operator	common carrier : air carrier
Make Model Name	Dash 8 Series Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	descent : vacating altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : cfi pilot : atp
Experience	flight time last 90 days : 200 flight time total : 7500 flight time type : 800
ASRS Report	484080
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : company policies non adherence : far other anomaly other
Independent Detector	aircraft equipment : gpws other flight crewa
Resolutory Action	flight crew : returned to original clearance flight crew : took evasive action
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

We were operating flight from sea to pdx. During initial approach, we were cleared to descend to 2000 ft MSL (approximately 1900 ft AGL). At about 2300 ft MSL, the GPWS sounded ('terrain, terrain, pull up, pull up'). I began an immediate climb, and the warning ceased by about 2500 ft. The radar altimeter never indicated less than 2000 ft AGL. I was sure of our location and of the terrain below, so I resumed our descent, and continued the approach and landing. However, when we informed ATC of our climb, we were simply reclred to 2000 ft and cleared for the ILS approach to runway 28L(?). During discussion of the event with ATC and the first officer, I inadvertently descended to about 1800 ft. We noticed the deviation and returned to 2000 ft to commence the approach. Due to the descent rates used and the terrain variations in the area, I was not sure that the GPWS warnings was erroneous. I, therefore, chose not to document the incident as an equipment failure.

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Original NASA ASRS Text

Title: A DHC8 FLC EXPERIENCED A FALSE WARNING FROM THEIR GPWS AND FAILED TO NOTE THE ANOMALY IN THEIR LOGBOOK AFTER FLT TERMINATION AT PDX, OR.

Narrative: WE WERE OPERATING FLT FROM SEA TO PDX. DURING INITIAL APCH, WE WERE CLRED TO DSND TO 2000 FT MSL (APPROX 1900 FT AGL). AT ABOUT 2300 FT MSL, THE GPWS SOUNDED ('TERRAIN, TERRAIN, PULL UP, PULL UP'). I BEGAN AN IMMEDIATE CLB, AND THE WARNING CEASED BY ABOUT 2500 FT. THE RADAR ALTIMETER NEVER INDICATED LESS THAN 2000 FT AGL. I WAS SURE OF OUR LOCATION AND OF THE TERRAIN BELOW, SO I RESUMED OUR DSCNT, AND CONTINUED THE APCH AND LNDG. HOWEVER, WHEN WE INFORMED ATC OF OUR CLB, WE WERE SIMPLY RECLRED TO 2000 FT AND CLRED FOR THE ILS APCH TO RWY 28L(?). DURING DISCUSSION OF THE EVENT WITH ATC AND THE FO, I INADVERTENTLY DSNDED TO ABOUT 1800 FT. WE NOTICED THE DEV AND RETURNED TO 2000 FT TO COMMENCE THE APCH. DUE TO THE DSCNT RATES USED AND THE TERRAIN VARIATIONS IN THE AREA, I WAS NOT SURE THAT THE GPWS WARNINGS WAS ERRONEOUS. I, THEREFORE, CHOSE NOT TO DOCUMENT THE INCIDENT AS AN EQUIP FAILURE.

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.