[A Boeing 737-400 started its take off roll with the F/O as PF. The crew were unaware that an electrical fault had moved its rudder trim from neutral to full scale left. The rudder trim had been confirmed at neutral before engine start. It takes 29 seconds for the rudder trim to move from neutral to full scale in one direction. The only clue would be a slightly offset rudder pedal position which could easily go unnoticed. During the early part of the take off run the aircraft started to drift left of the runway centreline; enough to concern the PF which he voiced to the captain. With the aircraft accelerating, a short discussion took place between the two pilots culminating in the captain taking over full control. He was able to track back towards the centreline and made the decision to abort but did not commence the abort procedure including reverse thrust and braking, until on the centreline. Earlier in the beginning of the take off roll there was a delay before full power was selected due to a problem with the autothrottle selection. That delay used up more runway. The result was the aircraft overran the far end and went into a river causing fatalities.
That’s a fascinating report. The bit that fascinates me particularly is that it didn’t need to be an RTO. That aircraft could have flown quite safely with rudder input, and the required rudder input would have been established during the takeoff roll as it would have during a normal crosswind takeoff.
How many B737 pilots actually understand how their rudder trim works? Boeing doesn’t help too much in the manual to be honest.
The answer is, in practicality, all the rudder trim does in a 737 is displace the rudder pedals. That is an excellent engineering design, because it draws immediate attention to the pilot that the trim is in place - providing the pilot has their feet on the rudder pedals.
It is also immediately overridable, merely by centreing the rudder pedals, and this does not require much force. It also does not limit full opposite rudder operation. A 737 could takeoff with full left rudder trim, suffer a left engine failure near V1, and reject or takeoff quite safely.
The only clue would be a slightly offset rudder pedal position which could easily go unnoticed.
This statement in the report is quiite confusing. “Slightly offset”?
Given what we now understand as to the function of rudder trim in a B737, which was it? Full runaway trim as stated in the report would result in full (or close to full) rudder pedal displacement. I would assume that no respected 737 pilot would advance to takeoff thrust without his feet on the rudder pedals, and if he had his feet there surely he would have immediately noticed the anomaly. I restate my fascination with the above report.
P.S. I note you have provided a link to the full report. I have not read it yet.