Bell 212 Over torque query

[walidKh]

What conditions causes an over torque of the PT6T3B engine on the Bell212 during 1st engine start, a sudden harsh yaw to the right was experienced corrected with a left pedal and resulted in an over torque in the 1st starting engine, please advice thanks in advance
Parameters from the smart cycle were as follows:
N1=93%
N2=48%
ITT= 718
and the over torque value =82.26%

[gulliBell]

Those parameters mentioned do not make sense to me: to get 80+% Tq out of a single power section the ITT has to be hotter than that..

The B212 can yaw on it's skids when the engine N2/NR is abruptly accelerated, and if it does the corrective action is to reduce application of the throttle.

If the engine has accelerated for unknown reason during start then maintenanance investigation is warranted.

If you suspect any exceedance of operating pararameters these should be mentioned to the maintenance engineer who will check relevant limitations in the maintenance publications.

[albatross]

Were the blades accelerating as normal.
Don't know if it is possible but could you have had a freewheel slip/hard engagement.
Possible when starting the second engine but have never heard of it happening on starting the first engine.
Strange one for sure.

[SASless]

That is a strange one.....as Albatross says.....maybe on the second engine start but on the first that is unusual.

I am curious what the engine gauges showed concerning rates of increase and such as much as the numbers they reached.

Also....how much throttle friction was applied....too little friction can allow quicker throttle movement than desired.

[tottigol]

Was the throttle brought back to idle or rolled all the way to flight?

[gulliBell]

There has obviously been a large input of engine power into the powertrain for the aircraft to yaw on the ground, however again I mention the observed engine operating parameters just don't make sense to me. I'm assuming the OP saw some sort of very short duration power spike during starting, and to me that indicates a malfunction in the AFCU that warrants investigation. With such a high Tq value observed at (presumably) flat pitch setting the NR would accelerate past 48% very quickly with sustained input of that power. I don't suspect some erronious high rate of throttle application caused this, from idle setting you can roll on a single throttle at any rate and the acceleration of the engine is governed, as long as you catch it before the N1 gets to 93% (usually it will take about 4 secs to accelerate to that N1 from idle with rapid application of throttle). That's how you do the acceleration check, and when you do it the aircraft doesn't yaw on the ground (assuming you are not on ice or wet steel deck when doing the check). I doubt the Tq figure reported because that number is in stark disagreement with the N1/ITT numbers. I also doubt that there is an actual overTq event here, but the reason for the uncommanded power input during start does need to be explored further (because it is unlikely explained by throttle application).

[Heliarctic]

The numbers donīt make much sense like GulliBell says.
It seems like some information is missing.

Could the GOV switch have been set to MANUAL by accident?
That could cause an uncontrollable acceleration, if the throttle isnīt managed carefully, but would very likely have showed higher ITT than the 718c written here.
HA

[gulliBell]

My concern in this instance would be the ITT peak during start: we know there was a large input in power due to the yaw reaction, for this amount of power the ITT must have been hotter than observed. There is unlikely to be an overTq event, but there may have been a hot start event that was missed because of the unexpected yaw distraction.

These things are best dealt with by the supervising maintenance engineer, they may see fit for a borescope inspection of the hot section.

[Salusa]

Walid, your quoted figures are pretty specific and you refer to"smart cycle parameters". Do you have a monitoring system installed?