Failure of all three engines as horizontal velocity approached zero or just before external tank jettison would also result in LOCV. The capsule communicator would call out the point in the ascent at which an RTLS was no longer possible as "negative return", approximately four minutes after liftoff, at which point the vehicle would be unable to safely bleed off the velocity that it had gained in the distance between its position downrange and the launch site. The RTLS abort mode was never needed in the history of the shuttle program. It was considered the most difficult and dangerous abort, but also among the most unlikely to occur as only a very narrow range of probable failures existed that were survivable but nevertheless so time-critical as to rule out more time-consuming abort modes. Astronaut Mike Mullane referred to the RTLS abort as an "unnatural act of physics", and many pilot astronauts hoped that they would not have to perform such an abort because of its difficulty. Transoceanic abort landing A transoceanic abort landing (TAL) involved landing at a predetermined location in Africa, Western Europe or the Atlantic Ocean (at Lajes Field in the Azores) about 25 to 30 minutes after liftoff. It was to be used when velocity, altitude, and distance downrange did not allow return to the launch point by Return To Launch Site (RTLS). It was also to be used when a less time-critical failure did not require the faster but more dangerous RTLS abort. For performance issues such as engine failure(s), a TAL abort would have been declared between roughly T+2:30 (two minutes 30 seconds after liftoff) and about T+5:00 (five minutes after liftoff), after which the abort mode changed to Abort Once Around (AOA) followed by Abort To Orbit (ATO). However in the event of a time-critical failure, or one that would jeopardize crew safety such as a cabin leak or cooling failure, TAL could be called until shortly before main engine cutoff (MECO) or even after MECO for severe underspeed conditions. The shuttle would then have landed at a predesignated airstrip across the Atlantic. The last four TAL sites were Istres Air Base in France, Zaragoza and Morón air bases in Spain, and RAF Fairford in England. Prior to a shuttle launch, two sites would be selected based on the flight plan and were staffed with standby personnel in case they were used. The list