DC8-73 takeoff clearance disputed by flight crew who all believed that they had heard the clearance. However, ATCT controller said they did not have clearance and issued advisory for wake turbulence of B747 departed ahead of them.

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Attributes
ACN	532292
Time
Date	200112
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : mmmx.airport
State Reference	FO
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tower : mmmx.tower
Operator	common carrier : air carrier
Make Model Name	DC-8 70
Operating Under FAR Part	Part 121
Flight Phase	climbout : takeoff ground : takeoff roll
Route In Use	departure sid : ns
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tower : mmmx.tower
Operator	common carrier : air carrier
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : initial
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : instrument pilot : multi engine pilot : cfi pilot : commercial pilot : atp
Experience	flight time last 90 days : 100 flight time total : 11000 flight time type : 4000
ASRS Report	532292
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	incursion : runway non adherence : clearance non adherence : far other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued advisory flight crew : took precautionary avoidance action
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Environmental Factor Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Approximately 20 KTS prior to V1 on takeoff roll, tower advised us to beware of wake turbulence of prior heavy departure. Then as we accelerated through V1, they continued and said that we did not have takeoff clearance. After rotation and cleanup (captain's leg), first officer told tower that we understood that we were cleared for takeoff. Tower responded that 'in the future please be careful of your takeoff clearance.' I maintained V2 +10 KTS to make sure we maintained horizontal and vertical separation with the previously departed B747. We had him both visually and on TCASII and maintained 5 mi separation. Once we got to a safe altitude and reduced workload, I queried the other 2 crew members whether or not they heard a takeoff clearance issued. They both said they did. I don't know why the discrepancy. Flight continued on to cvg without further comments from ATC and uneventfully.

Original NASA ASRS Text

Title: DC8-73 TKOF CLRNC DISPUTED BY FLC WHO ALL BELIEVED THAT THEY HAD HEARD THE CLRNC. HOWEVER, ATCT CTLR SAID THEY DID NOT HAVE CLRNC AND ISSUED ADVISORY FOR WAKE TURB OF B747 DEPARTED AHEAD OF THEM.

Narrative: APPROX 20 KTS PRIOR TO V1 ON TKOF ROLL, TWR ADVISED US TO BEWARE OF WAKE TURB OF PRIOR HVY DEP. THEN AS WE ACCELERATED THROUGH V1, THEY CONTINUED AND SAID THAT WE DID NOT HAVE TKOF CLRNC. AFTER ROTATION AND CLEANUP (CAPT'S LEG), FO TOLD TWR THAT WE UNDERSTOOD THAT WE WERE CLRED FOR TKOF. TWR RESPONDED THAT 'IN THE FUTURE PLEASE BE CAREFUL OF YOUR TKOF CLRNC.' I MAINTAINED V2 +10 KTS TO MAKE SURE WE MAINTAINED HORIZ AND VERT SEPARATION WITH THE PREVIOUSLY DEPARTED B747. WE HAD HIM BOTH VISUALLY AND ON TCASII AND MAINTAINED 5 MI SEPARATION. ONCE WE GOT TO A SAFE ALT AND REDUCED WORKLOAD, I QUERIED THE OTHER 2 CREW MEMBERS WHETHER OR NOT THEY HEARD A TKOF CLRNC ISSUED. THEY BOTH SAID THEY DID. I DON'T KNOW WHY THE DISCREPANCY. FLT CONTINUED ON TO CVG WITHOUT FURTHER COMMENTS FROM ATC AND UNEVENTFULLY.

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.