B757 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 211; Flight Crew Type 8239
Training / Qualification
Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented
Weather; Human Factors; Procedure
After completing our anti-ice at the gate in EGLL I requested via ACARS the hold over time. The message we received was telling us that the takeoff is prohibited. The conditions were temperature of 1C SNRA and visibility of 2400M. Under those conditions we all agreed that we should be getting some hold over time and based on experience we knew that we were probably in the neighborhood of an hour. After trying the ACARS procedure two more times with the same result; myself and the IRO using the Hold Over Time (HOT) app on our iPads independently determined the hold over time. Based on the above information and knowing that there was a line up for takeoff on 27R; Heathrow at the time was on a single runway operation; the Captain decided to disregard the ACARS message and use the app HOT. During taxi out the precipitation stopped and then by takeoff turned into rain. When number two for takeoff the Captain asked the IRO to perform a wing check which he did and found all visible surfaces to be clean. We took off inside the HOT determined by the app. Both I and the IRO have used the new procedure before; but this was the Captain's first time which made him question it when the result was obviously wrong.
[Report narrative contained no additional information.]
B757 flight crew reported deicing at the gate then requesting a hold over time via ACARS which indicated that takeoff was prohibited. They knew this was wrong and went to the iPad app and calculated a 75 minute HOT and departed. Once airborne they discovered that this type of conflict should have been resolved by contacting the Duty Manager.