V1 - That critical Sacred Cow.

[Centaurus]

It has always bemused me to watch some captains during the takeoff roll, put their hands over the top of the thrust levers in an unnatural claw-like grip as if to emphasis how ready they were to rip the thrust levers back to idle up to V1. There is no need for that nonsense. For example, a tyre burst 10 knots below V1 on a limiting length runway (be it wet or dry) followed by an abort, would risk the chance of an over-run due to lack of maximum braking availability. V1 is not the sacred cow of all possible takeoff go/stop situations.

For example, I was jump seating on a night take off in a 737-200 at an island in the Central Pacific. Runway was 5600 ft in length with no overun - only a 30 feet drop over a sea wall to the ocean below. The take off weight was limted by accelerate or stop criteria with max take off thrust with bleeds off at 2.18 EPR giving 100% N1.

Unbeknown to us, and because engine covers had not been put in place overnight, both of the engines Pt2 sensors were blocked by insects and dust from a nearby phosphate mine. The result was both EPR instruments over-read. This meant when the EPR showed 2.18 EPR, the real power was only around 2.08. That meant the N1 read about 85% N1 - not the 100% we expected. The engine gauges in the 737-200 were quite small and the difference between 100% N1 and 85% N1 was diificult to distinguish at night. with dim instrument lighting.

Early in the take off roll, both the captain who was PM and myself on the jump seat, had an uneasy feeling that something was not quite right as there wasn't the strong kick in the bum feeling we would have expected at 2.18 EPR. The fact that all gauge needles in both engines read the same, probably lulled us in the same sense of security. It wasn't until late towards the end of the take off roll it dawned on both the captain and myself there was no way the aircraft was going to get airborne by the end of the runway. With about three runway lights remaining and 10 -15 knots below V1, the captain urgently called "taking over" and slammed both thrust levers hard up against the mechanical stops and rotated to 15 degrees nose up. The acceleration increased markedly and we climbed into the totally dark night on instruments. Even after gear and flap retraction and climb power of 1.94 EPR set, the rate of climb was well below expected.

With 1400 nm to go to our destination of Guam in the Central Pacific, the captain made the decision to return to our departure base. Before that, a comparison made between the Operations Manual climb engine parameters and what our instruments showed, revealed a marked discrepency. In other words, we were considerably down on power on both engines. After the landing back on base, engineers discovered both Pt2 senors in the front of the cowls were blocked by insects and phosphate dust. We had experienced a similar problem as to the ill-fated Air Florida 737-200 that went into the Potomac River. In that instance the cause was traced to iced up Pt2 sensors and thus over-reading EPR gauges because the engine anti-ice had not been switched on.

What saved us was the decision by the captain not to abort even though we well below V1 and in theory should have beeen able to stop by the end of the runway. The decision to firewall the engines and thus get maximum power and rotate to 15 degrees early on rotation was the key to survival. When the sun rose in the morning after the take off, debris from footpaths over the road that passed a mere 20 feet from the runway end, was scattered down the runway. It was the closest shave I have ever experienced in my flying career.

Despite his quick actions in continuing the take off below V1, the captain was castigated by management for failure to pick up the discrepency between indicated EPR and N1 indications at the very start of the take off roll. Yet I too, had not picked up the discrepency although not wearing my glasses didn't help either. That incident was a classic example of being wise after the event.