MAS Twin Otter lands short?

[ManaAdaSystem]

A MASWings Twin Otter has landed short of the runway in Kudat. They call this an incident, but then talks of the crash site?
No fatalities as of now.

[ManaAdaSystem]

MASWings' Twin Otter aircraft crash lands in Kudat - Latest - New Straits Times (http://www.nst.com.my/latest/maswings-twin-otter-aircraft-crash-lands-in-kudat-1.372766)

Landed short or overshot the runway?

[DaveReidUK]

Landed short or overshot the runway?Neither, judging by this photo:

http://www.thestar.com.my/~/media/Images/TSOL/Photos-Upload/From%20DCX/Sabah%20plane.ashx?w=620&h=413&crop=1&

The partially-demolished house appears to be the one at 6.9242 116.8353, which is about 180m abeam the runway, about a third of the way from the 04 end (the airfield is behind the house, on the far side of those trees).

The article accompanying the photo, at

Three injured as plane skids off runway in Sabah - Nation | The Star Online (http://www.thestar.com.my/News/Nation/2013/10/10/Sabah-plane-skids.aspx)

talks about skidding off the runway, though the damage to the house would suggest that the Twotter was airborne when it hit.

[BOAC]

Seeing the pic of the front half of the a/c, if that is a pilot they are helping to walk over the fence.................................???

[Little Birdie]

The captain can still walk! Phew.

[ManaAdaSystem]

1 fatality, 5 wounded.

[WSSS]

It appears the FO has died of his injuries as well. The METAR from Avherald indicates wind gusts of up to 31 knots.

Accident: MASWings DHC6 at Kudat on Oct 10th 2013, impacted house (http://avherald.com/h?article=469b9009&opt=0)

[training wheels]

From the METAR:

WBKT 100700Z 27017G31KT 210V300 9999 SCT014 BKN280 30/24 Q1008

Using runway 22 gives a crosswind component of 13 knots from the right, yet the aircraft ended far to the right of the runway. Just seems a bit odd.

[The Ancient Geek]

The Twotter (or any STOL aircraft) is prone to being blown badly off course by strong crosswind gusts at low speed just before touchdown, there was a similar accident in Nepal a few months ago.

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.

[BOAC]

Agreed, but please check the numbers as per tw's post?

[Little Birdie]

From the METAR:

WBKT 100700Z 27017G31KT 210V300 9999 SCT014 BKN280 30/24 Q1008

Using runway 22 gives a crosswind component of 13 knots from the right, yet the aircraft ended far to the right of the runway. Just seems a bit odd.What are the chances of a failure in the starboard propeller pitch change mechanism causing it to reverse pitch?

[Super VC-10]

Aviation Herald reporting two fatalities.

[tdracer]

What are the chances of a failure in the starboard propeller pitch change mechanism causing it to reverse pitch?

I'm not familiar with what the Twin Otter was certified to, but I spent a bit of time working on a high-speed turboprop about 20 years ago. We were told to assume a propeller reversing pitch uncommanded would be catastrophic - in other words we needed to design for a probability of less than 10-9/hr.

[The Ancient Geek]

A strong gust from the right would whip the tail around leading to an excursion to the right. Geometry and surface areas.

[Rat Catcher]

It looks as if full flap is selected. On touch down with full flap, when you go into beta with a crosswind and you are not awake...:ooh:,
Some big teeth appear! Many worthy aviators have been chewed by the Twotter, one of the best lessons in directional control you can get...!:E

[cgwhitemonk11]

Yes the Twotter can be a bit of a handful in gusty conditions, but not if handled properly by a decent crew and not in those relatively mild metars, it is certified to do 27kts across.

Unless there was some sort of significant failure we are as of yet unaware of, this poor FO has lost his life for no apparent reason.

[The Ancient Geek]

Indeed, and when the going gets tough and the workload gets high it is easy to forget to check that the tiller is centred. Dont ask me how I know that.........

The Twotter is a fantastic aircraft but it has a few gotchas to catch the unwary.
The same, of course, applies to any STOL aircraft which operates routinely where most pilots would fear to tread.

[training wheels]

This photo shows the right wing completely severed from the fuselage and extensive damage to the cockpit. May well have impacted the ground right wing low with a pitch down attitude.

http://1-ps.googleusercontent.com/x/www.nst.com.my/w1.nst.com.my/polopoly_fs/1.372949.1381415837!/image/image.jpg_gen/derivatives/landscape_454/ximage.jpg.pagespeed.ic.KGyrU1YWeZ.jpg

This article from the local press (http://www.nst.com.my/latest/update-co-pilot-passenger-die-in-maswings-crash-in-kudat-1.372766) 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.

[Leftexit]

I often see the METARS reported as if they were the actual weather conditions at the time of the accident/incident. The conditions at the time of the event can be quite different to that of the previous/next METAR which are only reported every 30 minutes. Many airfields have rapidly changing conditions between MEATRS. I have seen 5 SPECIAL reports between METARS for visibility changes alone but these reports are not available on the normal weather web sites. I am not saying this was the case in this accident but generally METAR reports do not tell the full weather story.

[Piltdown Man]

When you lose control in a cross-wind it's normal to depart on the upwind side of the runway.

[Desert185]

"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.

[ManaAdaSystem]

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?

[cgwhitemonk11]

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. :uhoh:

Hopefully we find out.

[training wheels]

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.

Do they have a "non take-off configuration" warning indication on the DHC6? Full flap setting before take-off would have triggered it, if it did.

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.

[cgwhitemonk11]

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.

[DUSKY DOG]

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.

[walu]

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 Ancient Geek]

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.

[Desert185]

"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.

[acutabove007]

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:

Twin Otter - Engine failure on take-off - YouTube

as I see some talk on the possibility of an engine failure amongst other possibilities...

[Desert185]

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.

[The Ancient Geek]

(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.

[acutabove007]

@ 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?

[DaveReidUK]

when mixed with a gas turbine engines slower spool up timeFor a turbofan, certainly.

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.

[Desert185]

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.

[Escape Path]

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 agree on that one.

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? :uhoh:

[Iznogood]

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.

[Escape Path]

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)

Well I wouldn't know if I'd use zero flaps and 100kts on a 730m runway. Even more so if using flaps 20 helps me reducing my airspeed by 20kts (for stopping purposes). And I would definitely would have props on max from around 500ft AGL rather than after touchdown (considering this scenario) since first of all, I'd want to use reverse as soon as possible (which you can't do if you have props on max), not for stopping quickly but to cement the airplane on the runway: less airspeed would mean the wind would affect the aircraft less. Second, I'd like to keep as many options to control the airplane as possible, one of those being the use of beta (just past the stop, or a "prop blade disc" as they call it on the Dash 8) just before touchdown, and third, it gives me a quicker response, power wise, as I wouldn't have to fiddle (i.e. making larger adjustments) with the power levers as much as I would if I had the prop levers on minimum govern position.

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 :ok:

[surplus1]

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?

[essentialbus]

@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.