Originally Posted by
Flying Bull
Hi all
http://www.bfu-web.de/DE/Publikation...ublicationFile
page 12 following - findings to the accident.
The pilot increased the distance to a groundtarget sideslipping with a groundspeed of about 30 knots when the helicopter slowly turned sideways and increased turnrate, when going through 90 degrees - resulting in four and a half turns, before crashing with a high rate of decend.
Yes, actually turning clock-wise (to the right) as a torque reaction. And instead of immediately applying full left pedal to arrest the yaw rate, the pilot flying - upon realising the uncommanded yaw - decreased left pedal and actually applied right pedal.
The non-flying PIC apparently did not take over controls, neither did he call "left pedal". Rather he called "speed, speed, speed" (meaning "increase forward speed"), which as we all know is only the second or third response to uncommanded yaw (the primary response is to arrest the yaw with full, sustained opposite pedal, and - under certain circumstances - reduce power).
While it is a well-documented Fenestron issue that pilots do not apply enough, or quickly enough, or long enough, opposite pedal (but rather too little, too late), the pilot's response here of applying the *wrong* pedal is note-worthy.
The interim report implicitly links this wrong response to a German Police internal Safety Notice published a week before this accident (which was in force at the time of the accident and has since been corrected) which instructed to fly out of uncommanded right yaw by increasing forward speed and applying right (sic!) pedal.
The said Safety Notice was published after another police EC135 on 6 Feb 2016 encountered uncommanded right yaw. In that case the pilot was trying to transition from a high hover (1200' AGL) to forward flight by increasing power i.e. collective (as if transitioning in ground effect from a hover to forward flight) instead of simply applying FWD cyclic. Again, the helicopter behaved as expected with a torque reaction to the right.
However, instead of realising his/her mistake (of applying power instead of FWD cyclic) the pilot attributed the right yaw to the legendary "Fenestron stall" (which, as avid PPRUNE readers would conclude, doesn't exist). Hence the advise to reduce TR blade angle of attack by reducing TR power pedal (this in the EC 135 case that means less left rudder).
To rub this in: Not only did the pilot not realise his/her mistake at the moment when it happened in flight, but the incident was used to create the before-mentioned Safety Notice that established those unorthodox procedures to combat the legendary "Fenestron Stall".
The interim report implies that the actions or beliefs of both pilots of the occurrence helicopter (resulting in neither pilot taking corrective action to stop the yaw) were informed by this ill-fated Safety Notice that was circulated to all police pilots only a week before the accident.