An air carrier B737 flight crew, with radio communication problems, pushed back without a clearance.

Attributes
ACN	384470
Time
Date	199711
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : iad
State Reference	DC
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	ground : preflight 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 : 180 flight time total : 10000 flight time type : 300
ASRS Report	384470
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 240 flight time total : 6300 flight time type : 2100
ASRS Report	384951
Events
Anomaly	non adherence : published procedure non adherence : clearance non adherence : far other anomaly other
Independent Detector	other controllera
Resolutory Action	none taken : detected after the fact
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Prior to push back at iad, first officer called ramp control (129.55) from the gate for pushback clearance -- radio was weak, but readable. After 3 calls, both pilots understood ramp control to clear our flight for pushback. At no time during the push did ramp control attempt to stop our pushback or contact us. After completion of pushback, ramp control informed us that we had not been cleared for pushback. Poor radio reception resulted in miscom between aircraft and ramp control. Apparently, ramp control's instructions were blocked and crew only heard part of transmission that cleared flight for pushback.

Original NASA ASRS Text

Title: AN ACR B737 FLC, WITH RADIO COM PROBS, PUSHED BACK WITHOUT A CLRNC.

Narrative: PRIOR TO PUSH BACK AT IAD, FO CALLED RAMP CTL (129.55) FROM THE GATE FOR PUSHBACK CLRNC -- RADIO WAS WEAK, BUT READABLE. AFTER 3 CALLS, BOTH PLTS UNDERSTOOD RAMP CTL TO CLR OUR FLT FOR PUSHBACK. AT NO TIME DURING THE PUSH DID RAMP CTL ATTEMPT TO STOP OUR PUSHBACK OR CONTACT US. AFTER COMPLETION OF PUSHBACK, RAMP CTL INFORMED US THAT WE HAD NOT BEEN CLRED FOR PUSHBACK. POOR RADIO RECEPTION RESULTED IN MISCOM BTWN ACFT AND RAMP CTL. APPARENTLY, RAMP CTL'S INSTRUCTIONS WERE BLOCKED AND CREW ONLY HEARD PART OF XMISSION THAT CLRED FLT FOR PUSHBACK.

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.