Throttle lever error nearly destroyed Dash 8's engines
Propeller overspeed almost wrecked both powerplants after Widerøe crew pulled levers below flight-idle setting
Norwegian investigators have revealed that a Widerøe Bombardier de Havilland Dash 8-100 came close to double engine failure after the pilots inadvertently retarded the throttle levers to below the flight-idle position.
Both propellers were subjected to overspeed as the crew drew the levers back beyond a safety stop mechanism while reducing thrust in heavy turbulence.
The "uncontrollably high" rotation speeds, exceeding 1,500rpm, severely damaged the right-hand Pratt & Whitney PW121 engine, says Norwegian investigation board SHT, and only "mere chance" prevented similar damage to the remaining powerplant. SHT adds that the overspeed generated a "deafening" noise in the cockpit, rendering communication impossible.
During the incident the aircraft - which had been at 8,870ft (2,700m), descending towards Sørkjosen - lost 760ft in altitude before the crew regained control and shut the right-hand engine down. SHT says the pilots had to run through the shutdown procedure twice after missing a crucial propeller feathering step.
Protections include triggers under the levers and a warning sign
Flight-data recorder information shows the aircraft had banked more than 58˚ to the right, and pitched down by nearly 20˚, before returning to stable flight. It also drifted 30˚ off course. The crew opted to return to Tromsø, the departure point, and executed a single-engined landing. None of the 17 passengers and three crew members was injured.
Widerøe short-runway operations often require pilots to pull the throttle levers behind flight-idle on landing. The levers have a safety stop - a trigger which must be lifted 5mm - to prevent accidental selection during flight.
In its inquiry into the 21 February 2006 event, SHT has recommended Bombardier introduces "measures" to prevent propeller overspeed on the type.
Since February 2010, Widerøe has been modifying certain Dash 8s to reduce the risk of recurrence. The airline also points out that its Q400s have a different power lever function, which offers better protection than earlier Dash 8 variants.
I don't know about their DHC-8 but ours had a mechanical gate you have to get past by pulling some triggers before props go into ground pitch. In case you feel there need to go beyond that gate there are no fewer than three large and prominent placards warning of the horrible things that will happen if you should enter beta whilst in flight.
No amount of safeties can stop an unprofessional pilot at the controls from doing something stupid.
I think it's funny that the SHT would recommend Bombardier introduce measures to prevent Wideroe's idiot pilots from acting like idiots and exceeding the aircraft's capabilities.
It is one of the rules of basic design :- No matter how foolproof you make a simple control, the world will always manage to produce a better fool.
I knew a man who always squeezed the T handle of the auto transmission of his fancy car. It was only a matter of time before he went past N into R and wrecked the gearbox. The sad part is that he repeated this idiocy twice before selling the car as "a dud".
Last edited by The Ancient Geek; 4th Jul 2012 at 21:26.
Btw: Not sure.... who is the idiot pilot here.....
Thank you for posting that link.
I read the report and it doesn't appear there was any malfunction in the idle gates according to it. The report very clearly states that the pilot engaged the triggers in his reduction to flight idle, thus disabling the gate and putting the aircraft into ground idle. The report also stated that it this mistake was (essentially, I'm paraphrasing) caused by either panic or complacency. In my opinion any pilot that falls victim to either of those conditions is a fool, especially knowing through the mistakes of others that they are potentially deadly states of mind.
This crew took a bad event, severe turbulence, and created a catastrophic event through their own actions. A disturbing trend I've noticed in recent years are pilots in severe weather (usually turbulence) creating deadly or potentially deadly situations through careless actions or inability to manage the aircraft I'd be hard pressed to think of any time turbulence tore a plane apart, but I can name at least three instances in which a pilots reaction to said turbulence (or associated weather phenomena) did. I'm curious what has created this sudden shift in pilot mentality where now bumpy weather is something to fear?
Last edited by Island-Flyer; 4th Jul 2012 at 21:46.
Possibly not pilot error. In the Dash 8 (100/300), unless that power lever gate is set correctly, it is possible that rapid power lever movement to the flight idle stop will cause the PLs to "jump" the gate and go into discing. Also, sometime the trigger setting is set (badly) so that the slightest touch of either trigger will allow the PLs to pass the gate.
And that brings me to rapid power movement. I was taught that the only time you make a violent and rapid power lever movement was to avoid impact.
I don't blame the pilots exclusively though. I wonder what Wideroe's "unexpected turbulence encounter" procedure is. I know on jets our process was to deploy speed brakes prior to reducing power. Our company's turbulence encounter procedure reminds pilots to use the condition levers for more effective slowing to turbulence penetration speed, but I would imagine most pilots will go for the PL's first.
Again, this situation really didn't require any rushing. Hitting severe turbulence at 200 knots (versus 180) isn't going to destroy the plane. It's just really about slowing down. I'll digress on calling them idiots, this crew did their best and I hope they receive training to put them more at ease in abnormal situations. However one of my biggest pet peeves is the introduction of self-inflicted emergencies.
To this layman the power lever trigger does seem a bad design. Would appear easy to grab the whole thing in a brace reaction in turbulence. I think this section says it all...
2.2.4 It might be said that it requires more precision to grip the Power Levers without the fingers closing around the handles than it does to grip the entire mechanism. This factor is especially relevant when the aircraft is subjected to turbulence. The Accident Investigation Board can therefore understand how the Commander came to grip the entire mechanism, including the release triggers, when he suddenly had to pull back the Power Levers to Flight Idle. In this period, the g values were as low as -1.077. This can also result in a need to grip the handles extra hard. If the fingers grip the release triggers, the mass of the Commander’s right hand may itself provide enough force to release the stop function at a load of -1g. It is therefore understandable that the release triggers may have been lifted by accident when the Commander pulled the Power Levers to Flight Idle. A force of 2 kg, which is required to pass Flight Idle, cannot be said to represent certain assurance against the Power Levers being pulled too far back. This is especially true when the aircraft is being shaken hard in turblence.
2.2.6 The AIBN believes the Commander acted rationally when he gripped the Power Levers and pulled them back. He expected them to stop at Flight Idle, but ended up pulling them too far back.
PS I couldn't see a reference to lap straps in the report but perhaps I missed it.
......another tough guy shooting his mouth off without grasping the true picture! Your input has been thoroughly educational, probably for other macho Pilots.
Well for us weeklings the salient point of this incident is the power lever design and man/machine interface during severe turbulence. Specifically under negative G people will hook on to things for grip, unfortunately in this case the triggers. I've seen this happen, beta warning activated, I called it plus the type we were in wouldn't allow it in flight.....still a touching cloth moment!
Point is when hands and feet are flying through the air and you are trying to get your hands on the controls finess becomes near impossible 'as implied in the report'.
OK my pet peeve dealt with, 'macho pilots rubbishing fellow pilots'..... There but for the grace of god go we all!
OK my pet peeve dealt with, 'macho pilots rubbishing fellow pilots'..... There but for the grace of god go we all!
You can call it macho all you want and I'm not rubbishing them - I'm saying they screwed up and ruined a perfectly good plane through their actions. Do you disagree? We all face problems like severe turbulence throughout our flying career, if I were to destroy a plane in a turbulence encounter then I will expect to answer for my actions alone, and I would not allow my peers to point to a manufacturer as the cause.
In my opinion this is no different than AF447 of Colgan 3407 except that by the grace of god (as you put it) this crew didn't kill anyone. Crews on those flights, like this one, couldn't handle an abnormal situation and escalated it through drastic and incorrect control inputs. To caudle (sp?) them and act like they played no part in this accident does not help our profession one bit.
Engineers design aircraft to be flown by professional pilots, not to build triple redundant restrictions on normal flight controls to prevent a pilot from doing what he or she knows they should not be doing. If they made it harder to engage ground idle how long would it be before some yahoo runs a plane off the runway and I have to hear people defend him saying the triggers are too hard to engage?
Do I think this pilot should be hung out to dry? Absolutely not - I'm sure he rightly returned to the line and has been doing fine since. But I do think that if we sit here and state anything but the crew caused this accident we'd be doing a disservice to aviation safety.
Too often now low quality pilots are tarnishing our profession. We need to stop soft-balling them in the name of solidarity and start calling people on the crap they pull that puts the flying public at risk. If we as a community don't correct problems like that internally then it'll be left to the heavy hand of legislation (and to a degree it already is moving in that direction). Personally I'd rather we called a spade a spade and let this crew know they messed it up and retrain them accordingly than leave it to a bunch of engineers to make a band-aid fix on the DHC-8 to prevent a pilot from lifting the triggers, ignoring the warning bell, and moving the PL into ground idle.
Last edited by Island-Flyer; 5th Jul 2012 at 08:54.
Is this because more pilots are trained only in good WX conditions (South Africa and other places where long periods of predictable weather conditions pertain) so as to save money and get the pieces of paper quickly?
That seems to me to be a flaw in the philosophy of hiring noobs straight into an airline cadet scheme or similar. Where's the real breadth and depth of command experience going to come from for these people? I may be wrong and I will certainly listen to other opinions but in my gut I'd rather be a pax on a plane flown by a 10,000 hour pilot who had worked for a dozen different operators in half a dozen different countries than a 10,000 hour pilot who had done it all on "george" or the sim for the one outfit and on the one type. Extreme cases obviously, but you get my drift. Anyway, it's a bit of a side issue.
Haha Island-flyer, you make me chuckle Gotta love the in-depth analysis made from a pilot with location "hawaii" Just one question, do you have any experience whatsoever flying in the area where the incident took place?
what i am getting at is lifting the levers accidentally doesn't seem very possible so this captain may have done it on purpose
Its very possible, once the power levers are in the flight idle position the levers are easily within finger reach as intended after touchdown. In a stressful situation I can easily see the pilot lifting the levers and going past Flt Idle. A Dash went in in PNG recently with a similar story being the explanation. The natural reaction of Dash 8 pilot when needing to slow down on the ground is to pull the levers and go into disc or reverse, to say that this won't create a similar reaction in the air is denying a whole lot of human factor research.