The 80 knot call - potential for confusion?
In the B737 simulator the instructor can feed an airspeed error into the captain's or first officer's ASI. 25 knots is a fair and reasonable figure.
During take off the PNF calls 80 knots on his own ASI. By the time he actually annunciates the words his ASI is probably around 87 knots depending on speed of acceleration - especially if he had called a fraction late. I have never seen a call made when the ASI is less than 80 knots.
The PF who is steering the aircraft down the centre line glances at his own ASI to check the reading and sees a reading of 70 knots and accelerating. It might even be 98 knots and accelerating.
What to do? Abort or go? It is not a serious problem in itself as there is not only a standby ASI for comparison, but also various ground speed read-outs. It could be argued that as Boeing recommend that one should not abort for a Master Caution above 80 knots, then as the ASI problem is not serious (it just needs time to sort out the problem), the pilot should not abort because of an ASI discrepancy during the take off run above 80 knots.
We often see momentary confusion in the simulator when an ASI difference is picked up as the aircraft is accelerating quickly past 80 knots. Sometimes an abort is initiated and sometimes the PF will rotate on the "Rotate" call regardless of what his own ASI is reading. Quick thinking is needed.
Seems to me that by continuing the take off roll, there is more time available for the PNF to read the three ASI's and compare groundspeeds as well, and have a pretty good idea which one is wrong by the time the VR speed is reached. Much safer than a hasty abort that is not warranted? Any thoughts?
It is difficult to assess which ASI reading is faulty in the time available and often the best solution is to keep the aircraft on the ground longer than normal - but to always continue the take off roll rather than abort.