Narrative:

Already in position and hold, we (aircraft X) were cleared for takeoff behind a B747 (aircraft Y) that had just broken ground ahead. Part 1 refers to a 2 min or 4 or 5 mi separation for wake turbulence separation. We questioned our clearance and the tower insisted 1 mi separation was enough. Rather than get into a dispute over the air waves we elected to delay takeoff until we considered it safe. Unable to find wake separation notes on the united kingdom in part 2 at this time. We considered asking for 4 mi prior to taking the runway but felt assured lhr operated under a similar separation to the united states system.

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Original NASA ASRS Text

Title: B767 FLC QUESTIONS EGLL CTLR WHEN ISSUED TKOF CLRNC 1 MI BEHIND DEPARTING B747. FLC DELAYS TKOF UNTIL APPROX SEPARATION EXISTS.

Narrative: ALREADY IN POS AND HOLD, WE (ACFT X) WERE CLRED FOR TKOF BEHIND A B747 (ACFT Y) THAT HAD JUST BROKEN GND AHEAD. PART 1 REFERS TO A 2 MIN OR 4 OR 5 MI SEPARATION FOR WAKE TURB SEPARATION. WE QUESTIONED OUR CLRNC AND THE TWR INSISTED 1 MI SEPARATION WAS ENOUGH. RATHER THAN GET INTO A DISPUTE OVER THE AIR WAVES WE ELECTED TO DELAY TKOF UNTIL WE CONSIDERED IT SAFE. UNABLE TO FIND WAKE SEPARATION NOTES ON THE UNITED KINGDOM IN PART 2 AT THIS TIME. WE CONSIDERED ASKING FOR 4 MI PRIOR TO TAKING THE RWY BUT FELT ASSURED LHR OPERATED UNDER A SIMILAR SEPARATION TO THE UNITED STATES SYS.

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.