MAS Twin Otter lands short?
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Training Wheels
"This article from the local press reports that the accident happened during take-off and not landing, which brings up the possibility of a right engine failure after take-off. If so, and with wind gusts up to 31 knots, it would have been a huge struggle to keep it straight and maintain V2."
So why the full flaps? Normal takeoff is F10, and that is the desired flap setting with an engine out inflight. Doesn't compute unless they lowered flaps prior to touchdown...with doesn't necessarily compute.
Unless the autofeather was inop, a loss of power after V1 in a Twin Otter is manageable, assuming the airport is near sea level.
So why the full flaps? Normal takeoff is F10, and that is the desired flap setting with an engine out inflight. Doesn't compute unless they lowered flaps prior to touchdown...with doesn't necessarily compute.
Unless the autofeather was inop, a loss of power after V1 in a Twin Otter is manageable, assuming the airport is near sea level.
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Engine failure in go around? Could explain the confusion re landing/take off, and explain the flap setting.
Or just a screwed up go around?
Or just a screwed up go around?
Last edited by ManaAdaSystem; 11th Oct 2013 at 06:13.
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Just home after 6 sectors in virtually the exact same winds recorded during this tragedy, worse even if I'm honest, real handful and a strain on even a very senior training captain sitting on my left carrying out the toughest of the landings. But we never came within a million miles of leaving the runway, despite my best efforts.
Aside from the unusual Flap selection i think this is likely an EFATO gone wrong or potentially this could have happened:
Landed previous flight, forgot to retract flaps, rushed turn around, took off with Full Flap selected and rotated like a helicopter much earlier than expected and surprised the crew. Have had this done in training and if you are not expecting it is a BIG surprise.
Hopefully we find out.
Aside from the unusual Flap selection i think this is likely an EFATO gone wrong or potentially this could have happened:
Landed previous flight, forgot to retract flaps, rushed turn around, took off with Full Flap selected and rotated like a helicopter much earlier than expected and surprised the crew. Have had this done in training and if you are not expecting it is a BIG surprise.
Hopefully we find out.
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Landed previous flight, forgot to retract flaps, rushed turn around, took off with Full Flap selected and rotated like a helicopter much earlier than expected and surprised the crew. Have had this done in training and if you are not expecting it is a BIG surprise.
It's more likely a go-around that went horribly wrong, due to the gusty conditions. To drift that far off the runway for a normal landing attempt would be highly unlikely, and if the winds are reported correctly, they would have drifted to the left, not right of runway centreline.
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No take-off configuration warning on any of the ones I have ever been on. Poorly executed Go-Around a possibility, I know of someone who recently had a hydraulic failure on short finals which would have prevented a Go Around due to being unable to retract from Full Flap, also a possibility in this case.
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Reason for full flap""
Maybe knowing they were going down decided upon the full flap to get min speed.;prior impact.
However for directional control problems one cannot stress enough tail-dragger time before flying STOL type aircraft.
Maybe knowing they were going down decided upon the full flap to get min speed.;prior impact.
However for directional control problems one cannot stress enough tail-dragger time before flying STOL type aircraft.
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My thoughts go out to the co-pilot and the other fatality and injured. Just by looking at the aircraft reminds me of other twin otter crashes I have witnessed, it is still a very strong airframe though and people have survived remarkably well in accidents in this type.
The flap system, post crash with wing separation, will lose pressure/fluid and therefor the flaps will droop if not supported by something else. So you cannot draw conclusions just by looking at a couple of pictures ok.
Yes the flaps are a very important part of the Twin Otters capabilities and should be used according to the situation. Hard runways on wheels will not usually nesssistate the use of STOL config and you will gain enhanced crosswind authority if you use standard flaps 20 for landing and 10 for departure. But, having said this, there is still adequate control up to the cross wind limits using the STOL configuration. So it comes down to handling/technique and experience.
Lastly, operating next to coconut tree lined runways in heavy crosswinds isn't easy and sometimes down right tricky especially onto short wet runways.
My impression is they may have bounced on landing, got slow, attempted to go around and power came up differentially. Then a loss of airspeed may have led to wing stall and subsequent impact with ground.
I ain't no crash investigator but I can understand how these events can occur from personal experience and close observation. The Twin Otter is still marvelous but when I think back to my early days as a fresh FO on her I can remember how tricky it was to ease down during heavy crosswinds in wet runways.
The flap system, post crash with wing separation, will lose pressure/fluid and therefor the flaps will droop if not supported by something else. So you cannot draw conclusions just by looking at a couple of pictures ok.
Yes the flaps are a very important part of the Twin Otters capabilities and should be used according to the situation. Hard runways on wheels will not usually nesssistate the use of STOL config and you will gain enhanced crosswind authority if you use standard flaps 20 for landing and 10 for departure. But, having said this, there is still adequate control up to the cross wind limits using the STOL configuration. So it comes down to handling/technique and experience.
Lastly, operating next to coconut tree lined runways in heavy crosswinds isn't easy and sometimes down right tricky especially onto short wet runways.
My impression is they may have bounced on landing, got slow, attempted to go around and power came up differentially. Then a loss of airspeed may have led to wing stall and subsequent impact with ground.
I ain't no crash investigator but I can understand how these events can occur from personal experience and close observation. The Twin Otter is still marvelous but when I think back to my early days as a fresh FO on her I can remember how tricky it was to ease down during heavy crosswinds in wet runways.
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Stable crosswinds can be a bit challenging but are manageable. Unstable gusting crosswinds are a serious challenge with big teeth especially at short narrow strips.
This applies to all STOL aircraft, not only the Twotter.
This applies to all STOL aircraft, not only the Twotter.
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Walu
"The flap system, post crash with wing separation, will lose pressure/fluid and therefor the flaps will droop if not supported by something else. So you cannot draw conclusions just by looking at a couple of pictures ok."
Excellent point.
Excellent point.
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Not knowing much about the DHC6 from a pilots point of view, but other then what I read technically about flying the aircraft, can I ask: whats makes a STOL aircraft unable to perform under certain conditions that "a non STOL" aircraft can?
"This is one of the known risks of short landings in STOL aircraft into short narrow strips in unstable weather conditions. There is a short window just before touchdown where there is insufficient time for a go-around and an incident is inevitable if a sudden gust bites you."
Could someone explain this paragraph as im very interested in this, as I'll hopefully be flying the Twotter in the not to distant future and therefore any more info would be beneficial.
Not sure if anyone has seen this:
as I see some talk on the possibility of an engine failure amongst other possibilities...
"This is one of the known risks of short landings in STOL aircraft into short narrow strips in unstable weather conditions. There is a short window just before touchdown where there is insufficient time for a go-around and an incident is inevitable if a sudden gust bites you."
Could someone explain this paragraph as im very interested in this, as I'll hopefully be flying the Twotter in the not to distant future and therefore any more info would be beneficial.
Not sure if anyone has seen this:
as I see some talk on the possibility of an engine failure amongst other possibilities...
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acutabove007
I used to fly a Twin Otter, a Beaver, Super Cub, etc. I never considered myself a hardcore bush pilot even though I still fly a 185 with Sportsman cuff, WingX and VG's in the backcountry. I also don't understand the comment as to why "STOL" aircraft are different. Maybe we'll get an explanation.
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(Could someone more current please correct this if necessary - it was a long time ago - thanks)
As I remember it :-
The problem is the relatively low inertia in a slow STOL landing versus the wind against a large side cross section and full flaps. Any unstable wind vector is going to have a large effect and you dont have enough energy to punch through it. As you approach touchdown point you are close to a stall and the turbine engines are not going to spool up fast enough to save you if the wind throws you around.
You are about to put your wheels on the ground wherever the wind surprise has put you, usually pointing in a bad direction. The power that you added to attempt a go around will now arrive and make matter worse.
A constant crosswind is manageable within the limits of the aircraft but strong and unstable gusting crosswinds are downright dangerous.
As I remember it :-
The problem is the relatively low inertia in a slow STOL landing versus the wind against a large side cross section and full flaps. Any unstable wind vector is going to have a large effect and you dont have enough energy to punch through it. As you approach touchdown point you are close to a stall and the turbine engines are not going to spool up fast enough to save you if the wind throws you around.
You are about to put your wheels on the ground wherever the wind surprise has put you, usually pointing in a bad direction. The power that you added to attempt a go around will now arrive and make matter worse.
A constant crosswind is manageable within the limits of the aircraft but strong and unstable gusting crosswinds are downright dangerous.
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@ the ancient geek
That sounds like a pretty damn good explanation and thanks, as I now understand that a little better.
so to conclude STOL aircraft are near (or nearer) the stall condition (slow speed) when over the threshold and that when mixed with a gas turbine engines slower spool up time (comparison to piston) equals where the danger is...
So would it be correct to say that piston engine STOL aircraft are slightly easier to manage and suffer less in these conditions?
That sounds like a pretty damn good explanation and thanks, as I now understand that a little better.
so to conclude STOL aircraft are near (or nearer) the stall condition (slow speed) when over the threshold and that when mixed with a gas turbine engines slower spool up time (comparison to piston) equals where the danger is...
So would it be correct to say that piston engine STOL aircraft are slightly easier to manage and suffer less in these conditions?
Last edited by acutabove007; 15th Oct 2013 at 16:57.
when mixed with a gas turbine engines slower spool up time
But SOP on the PT6-powered aircraft that I have encountered is to use the prop levers to set the prop (and the corresponding engine) RPM on final approach,so that the need to spool up the engine core didn't arise - 1675 PRPM rings a bell on the Shorts 360, for example.
I have no experience of the Twotter, but of course that has PT6s too.
Last edited by DaveReidUK; 15th Oct 2013 at 17:32.
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The Ancient Geek
I dunno. Slow is slow, regardless of STOL, piston, turbine or even a 747 (although, I'd rather be in a 747 during a gusty XW).
Generally, there is always going to be a headwind component, so even adding a bit of speed for the gusts won't be a factor for landing distance. In the Twin Otter during a gusty crosswind I would use F20 instead of full flaps. Reverse, flaps up, braking as required depending on the surface still resulted in a fairly short rollout even with less flap. Engine responsiveness (or lack thereof) never seemed to be an issue.
I suppose if you're 'on the edge' with really bad gusts there would be a problem, but the reality is a shorter landing distance with more headwind component. Limits exist with any airplane.
Generally, there is always going to be a headwind component, so even adding a bit of speed for the gusts won't be a factor for landing distance. In the Twin Otter during a gusty crosswind I would use F20 instead of full flaps. Reverse, flaps up, braking as required depending on the surface still resulted in a fairly short rollout even with less flap. Engine responsiveness (or lack thereof) never seemed to be an issue.
I suppose if you're 'on the edge' with really bad gusts there would be a problem, but the reality is a shorter landing distance with more headwind component. Limits exist with any airplane.
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In the Twin Otter during a gusty crosswind I would use F20 instead of full flaps. Reverse, flaps up, braking as required depending on the surface still resulted in a fairly short rollout even with less flap. Engine responsiveness (or lack thereof) never seemed to be an issue.
I will also add to the "why is it different with STOL aircraft?" explanation one more factor: Approach angle. Landing with full flaps you will be coming with the characteristic nose low approach on the TwOtter; that makes the flare more difficult since obviously you don't want to hit the nose and it is in that window, which emerges from the somewhat extended exposure time to the high winds with low airspeed in the flare, which I think makes it all a tad more difficult and that at some point has catched anyone who has flied the TwOtter. Hence the reason I support Desert's post on using flaps 20 on windy/gusty days.
A quick search on Wikipedia showed that Kudat runway is 730m long. AvHerald says there 14+2 on board; add that to a fuel load of say a 30min flight plus alternates and such and there's a landing weight of around 12000lb? The speed difference between full flaps and F20 at those weights is only 7 knots, F20 Vref at those weights usually being 79kts, which for a 730m tarmac runway is plenty enough, plus having the bonus of approaching with a more "normal" angle which would make the flare easier and quicker plus, as others said, increased rudder authority. And also if you add a bit of beta just before touchdown, just past the stop, will have you making a firm but quick(!) landing.
I don't like to make judgements on situations I haven't been in, but dare I say perhaps full flaps wasn't the best choice for this scenario?
Last edited by Escape Path; 4th Nov 2013 at 02:37.
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Ideal landing with DHC 6 in cross wind is flaps 10/speed 85. Or even flaps 0/speed 100/condition levers max after touchdown if runway lenght permitting.
Best technique to maitain axis: keep the nosewheel up by pulling progressively the control column vs decreasing of speed as far as possible (it will drop by itself at around 50 -40 kts)
Below this speed you can stop the DHC 6 easilly.
Best technique to maitain axis: keep the nosewheel up by pulling progressively the control column vs decreasing of speed as far as possible (it will drop by itself at around 50 -40 kts)
Below this speed you can stop the DHC 6 easilly.
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Ideal landing with DHC 6 in cross wind is flaps 10/speed 85. Or even flaps 0/speed 100/condition levers max after touchdown if runway lenght permitting.
Best technique to maitain axis: keep the nosewheel up by pulling progressively the control column vs decreasing of speed as far as possible (it will drop by itself at around 50 -40 kts)
Best technique to maitain axis: keep the nosewheel up by pulling progressively the control column vs decreasing of speed as far as possible (it will drop by itself at around 50 -40 kts)
I also wouldn't like to play with the airplane in zero flap config in speeds nowhere near those you mention (40-50) with around 12000lbs GW (according to my numbers), let alone in gusting conditions, since max weight stall speed (clean config) is 74kts. Just my 2c worth though
BTW, we have prop levers, not condition levers, on the Otter since we also have fuel levers
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Pure speculation -
Runway relatively short
Winds high, gusty, crossed
Configuration normal for landing
Airspeed a bit higher than normal due to winds
touched down just a tad longer than desired. Pilot eager to stop asap selects hard reverse. #2 prop reverses, #1 does not. Aircraft turns hard right and exits runway.
Comments?
Runway relatively short
Winds high, gusty, crossed
Configuration normal for landing
Airspeed a bit higher than normal due to winds
touched down just a tad longer than desired. Pilot eager to stop asap selects hard reverse. #2 prop reverses, #1 does not. Aircraft turns hard right and exits runway.
Comments?
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@surplus1
Interesting theory, but very likely?
Read post #13
Further, i tend to be more with the posters of @27 and #32.
That would make more sense in a possible clarification as how the aircraft ended up where it was, about 200 meters right side of the runway with a gusty crosswind from the right.
But, all speculation aside, on post #3 there is a picture of two firemen helping the PIC walk away from the aircraft.
So, you have a PIC who can be interviewed, the wreckage is available for investigation, then it should not take an investigation team very long to come to an at least priliminary report?. And then we should know.
But so far, nothing heard.
Interesting theory, but very likely?
Read post #13
Further, i tend to be more with the posters of @27 and #32.
That would make more sense in a possible clarification as how the aircraft ended up where it was, about 200 meters right side of the runway with a gusty crosswind from the right.
But, all speculation aside, on post #3 there is a picture of two firemen helping the PIC walk away from the aircraft.
So, you have a PIC who can be interviewed, the wreckage is available for investigation, then it should not take an investigation team very long to come to an at least priliminary report?. And then we should know.
But so far, nothing heard.