An air carrier medium large transport crew climbed in response to a false GPWS warning.

Attributes
ACN	283711
Time
Date	199409
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : lrp
State Reference	PA
Altitude	msl bound lower : 9000 msl bound upper : 9500
Environment
Flight Conditions	IMC
Aircraft 1
Controlling Facilities	tower : orf
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	other
Route In Use	enroute airway : phl
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	283711
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe 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 : returned to intended course or assigned course none taken : anomaly accepted
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 1000
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Arrival into phl, holding at bucks intersection, 9000 in moderate occasional heavy rain. Just as we entered hold in left turn we got terrain warning 3 times, aural and lights, followed by 'whoop, whoop, pull up!' twice. I knew we were at 9000 ft but we were in heavy clouds and rain. I disconnected the autoplt and initiated climb. We called ATC and informed them. After climb of 400-500 ft. We returned to 9000 ft. Discussed with ATC and figured there was an aircraft directly below us 1000 ft. The warnings were realistic as 3 terrain warning followed by GPWS pull up. After returning to 9000 ft flight continued normally.

Original NASA ASRS Text

Title: AN ACR MLG CREW CLBED IN RESPONSE TO A FALSE GPWS WARNING.

Narrative: ARR INTO PHL, HOLDING AT BUCKS INTXN, 9000 IN MODERATE OCCASIONAL HVY RAIN. JUST AS WE ENTERED HOLD IN L TURN WE GOT TERRAIN WARNING 3 TIMES, AURAL AND LIGHTS, FOLLOWED BY 'WHOOP, WHOOP, PULL UP!' TWICE. I KNEW WE WERE AT 9000 FT BUT WE WERE IN HVY CLOUDS AND RAIN. I DISCONNECTED THE AUTOPLT AND INITIATED CLB. WE CALLED ATC AND INFORMED THEM. AFTER CLB OF 400-500 FT. WE RETURNED TO 9000 FT. DISCUSSED WITH ATC AND FIGURED THERE WAS AN ACFT DIRECTLY BELOW US 1000 FT. THE WARNINGS WERE REALISTIC AS 3 TERRAIN WARNING FOLLOWED BY GPWS PULL UP. AFTER RETURNING TO 9000 FT FLT CONTINUED NORMALLY.

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.