View Full Version : Saab 340 incident report clarification needed

23rd Apr 2012, 16:33
Just finished reading a runway excursion report and I need abit of clarification. It says one of the propellers auto-coarsened at touchdown due to an intentional power lever split for a crosswind landing.

Is auto-coarsening an autofeather situation?


Autocoarsen Activation and Its Timing
(1) Based on the descriptions in 2.13.2 @<hidden>, it is considered probable that the actual angles of the power levers between 11:26:13 and 11:26:14 met the autocoarsen activation condition (PLA > 64 degrees).

(2) During the period between 11:26:13 and 11:26:14, the left engine torque was below 50% while the right engine torque was above 50%. At 11:26:13, the torque differential between the engines was 29.1% although at 11:26:14 it was 23.2%, a level slightly below the autocoarsen activation threshold. It is therefore considered probable that the torque differential met the autocoarsen activation condition in this 11:26:13 to 11:26:14 period.

(3) In the period between 11:26:12 and 11:26:14, the right engine P3 rose above 150 psi while the left engine P3 remained below 145 psi. It is therefore considered probable that the P3 sensor switch trip threshold (i.e., 145 psi maximum) for pressure rising condition described in 2.12 (2) was met.

As described above, it is considered highly probable that around the period between 11:26:13 and 11:26:14, the Aircraftfs left engine met the autocoarsen activation conditions in HIGH POWER mode. This is also supported by a sharp rise in torque and a drop in propeller speed of the left engine in addition to a sound suggesting decreased propeller speed, which were recorded for this period by the DFDR and CVR, respectively. It is therefore considered highly probable that the left propeller was brought to the coarsen pitch at that timing.

23rd Apr 2012, 17:21
Auto-coarsen is basically an auto-feathering device. When the propellor drops below certain parameters, it will feather the propeller. It's usually used during take-off or landing.

23rd Apr 2012, 17:48
Not truly feathered, it spins IIRC 80-800 rpm. When it gets enough oil pressure from the faster spinning, it goes back to coarse, cycling.

Since the Aircraft touched down in a right wing row attitude, the right main gear contacted the runway first, followed by the left main gear, and then the nose gear.

Ah, Japan.

I dont use the brake pedals while controlling the rudder, because doing so is rather difficult.


24th Apr 2012, 03:36
Autocoursen is advertised to be a lower-drag condition than full autofeather. Whether this assertion is factual, I cannot say.

SEO by vBSEO 3.6.1