Let410 V. Dhc-6

[Soap Box Cowboy]

There has been an intresting debate going on in the "LET off the Runway in Tanzania" post. I thought the way it had started going it was time to start a new post regarding Let's versus Otters. I've copied some of the data I submited on that post here, but you can also check out over there what has been said so far.

Look forward to hearing everyone's stories and views on this subject, which I'm sure is of intrest to all of us operating in Africa. Usually these things dislove into :mad: contests but hopefully we will getsomething usefull before it all goes too crazy :\





Well statistics are a wonderfull thing and so easy to manipulate.

Here are a few tid bits I found whilst researching this subject.

LET 410 design was started in 1966, with the prototype flying in 1969. But production was not started till 1971 due to problems with the initial prototype aircrafts (Excesive airframe vibration and cabin noise, Fixed on prototypes three and four). Initial versions are powered by two PT6A-27's. Then switched to Walther 601's.

Here are the versions:

L-410A 27 built and are equiped with PT6's

L-410AF 1 built supplied to Hungary, Aerial survey version with glazed nose.

L-410M 109 built first version with M601A engines producing 735 ESHP each.

L-410UVP 495 built A stretched version of the origional LET with larger wings and increased Fin and Rudder. Production ceased in 1985.

L-410UVP-E 370 built by mid 1990. Larger engine's and tip tanks fitted, plus interior modified for 19 pax instead of the orgional 15 and accomidation for two crew.

Series production reached 1000 by the end of 1990, of these 300 were for the Military.

Design work for the Twin Otter was started in 1964 with the first prototype flying in 1965 with first deliveries in 1966. By 1974 410 twin otters had been sold operating in excess of 2.3 million hours. Production was ceased in 1988 with 844 built.

Here are the versions:

CC-138 3 built. Initial version powered by two PT6A-6 engines (579 ESHP).

DHC-6-100 115 built. Short nose version with PT6A-20 engines (579 ESHP) Production completed in 1968.

DHC-6-200 115 built. Long nose version and higher gross weight option of the -100. Also available with short nose for float operations. Production completed in 1969.

DHC-6-300 613 built. Equiped with two PT6A-27 engines (652 ESHP). Increase take-off weight of 1000 lbs. Also available with a ventral baggage pod and as a water bomber. Short nose available for float version.

DHC-6-300M/MR 1 built. Designed as a military transport or Coin version with Cabin mounted machine guns and underwing hard points. Only one built and was delivered to Senegal.

DHC-6-400 0 built. Proposed developlment to meet US FAR 36 regulations, never built.

Now I agree with Solid Rust Twotter that the two aircraft were designed for totally diffrent operating enviorments. The Otter is a true bush plane, whilst the Let is a wanna be bush plane. The otter is great for the bush since you can take it anywhere, hence the increased hull loss. It operates in a riskier enviorment. But the Let beats the Otter hands down in the regular commuter market, it's faster and has a larger cabin.

Does anyone have the statistics of Hull loss per operating hour? And perhaps a breakdown of the cause of hull losses and locations. And perhaps some figures on dispatch reliability, operating cost, and some perhaps some stories from the guys who have flown the aicraft and can tell us what they think each aircraft is capable of. Or perhaps someone who has flown both and would like to offer an opinion of which they think is best.

Though getting accurate hours data for teh Let 410's may be har since some of the operators are less than truthfull :E

Seems the statistics might already be flawed :(

[let410fly]

SBC it's no contest!

"whilst the Let is a wanna be bush plane"

Take an incident in Algeria:

LET went off the runway into sand, and was then pulled out to fly away without any problems. The Otter opposition made a big song and dance about it.

A few weeks later, an Otter did the exact same thing, but the wing came off, with the prop giving the F/O a close haircut. Not a word from them about it. In fact the accident was listed as having taken place in Spain.

[Shrike200]

I tend to agree with the original post. I had the pleasure (?) of operating Twotters from Loki into Sudan (as well as flying in Algeria and Burundi), and I just can't see that a Let could have survived all we threw at those poor Twotters in Sudan. They would have just settled onto their bellies in the mud! So, in true rough-field, poorly prepared surface operations, the Twotter wins hands down, IMHO. Also, I think the Twotter is the clear winner in the STOL department. But if runway length and surface are not limiting for the Let, then it's slightly higher speed and cabin capacity certainly count for lots of points.

I can't really comment on maintenance aspects - that probably has a lot to do with the indivdual operators, perhaps so much so that a clear picture would be difficult to build up in the African context. Pilot skill/training/competency/currency would also play a large role when comparing statistics of incidents and accidents between the types. I believe most Twotter accidents (in Africa) tend to be the low speed take off and landing type, running off the RWY etc. I did some searching on this subject whilst doing my Twotter conversion, but I can't give any references unfortunately. I personally have heard of FAR more fatalities in Lets than Twotters in Africa, but that may just be due to above factors, and the greater safety margin the Twotters STOL abilities give it when departing African strips. Assuming both engines keep working! (A Twotter on one at MTOW is marginal at best, but then again the Let probably is too!)

The closest I've come to Lets is taxiing in the cockpit of one of the 420's in Algeria when I flew Twotters there, so I can't really comment on operating the Let though.

So, to sum up - if the fields are really rubbish (ie bad surface and short) then you have to have a Twotter. If not, you'd have to look at loads, sector times, costs etc.

My personal experience of the Twin Otter is that its very rugged, especially its undercarriage, generally very reliable (there isn't too much to break!) and a plane with a really great character. I liked it, and its strengths have saved my butt more than once.

[propspanner]

:yuk: :yuk: :yuk:

The only "good thing" thats what the pilot's have to say??

Is.....

The LET has spoilers :zzz:
and
Water injection :ok:

Other than that, there is not much :{

It looks like a flying fidelity gaurd van. Look at the front cocpit windows :}

And then the MMWC are putting PT6 in??? wonder why??
Make it go faster?
They should put the Walter in as a GPU :ok: thats all what it is good for.

Cheers E 20....mm sorry E 40 driver!

[chuks]

I have a fair amount of time in the Twin Otter. The LET I have only sat in, parked.

The main problem I have noticed with the Twin Otter is that it can be a bit of a handful in crosswinds. Low-time guys seem to find it a handful, especially if they are used to something like a Cessna 402, say. The Cessna just lands and sits there, with its low wing and short gear. The Twin Otter will quite happily try to groundloop if you let it. Every so often you hear of this or that unfortunate who has managed to grind off the outboard aileron hinge when his Twin Otter got away from him.

Handling aside, I have found the Twin Otter to be a very rugged and user-friendly aircraft. I really enjoyed my time on the type.

Well, I do have tinnitus in my left ear, which cropped up after my last tour flying the type, so that cockpit noise certainly doesn't meed modern expectations. There was this one car at Warri Airstrip equipped with an alarm that would go off every time a Twini Otter took off. Now that is loud! Here in Germany they have to be equipped with a four-bladed prop modification to meet the noise standards.

And with the low wing-loading you were in for a rough ride in turbulence, so that the pax were often not very impressed with the job you were doing, try as you might.

[wheels up]

Oh yeah, Propspanner, DEON DU PLESSIS, stirring again. Spent a bit too long in the Hassi sun??

You left out the anti-skid, autofeather, IELUs (engine parameter limiters) and ABCs (anti-yaw) by the way.

Baaaaaad Engineer. DOWN!

Well the Twin Otter does not exactly rate as the greatest looking aircraft ever designed. Looks like the nosewheel came straight off a wheel barrow. As for the high-tech wing enlarged from a cherokee 140 with it's high performance 1930 s Clark Y wing section that can't even support itself without great big struts...and even those have to be inspected on a regular basis to stop the wings falling off.

Then again, the Twin Otter can't be a bad aircraft or they wouldn't have built so many. It has a market niche that not many aircraft can compete in.

Can't say I disagree about the security van windshield comment, although the record in Algeria speaks for itself - windshields desteoyed: Let 0, Propspanners' aircraft, 2 down! Then again, a security van windshield is probably not a bad idea in Africa. Typical soviet approach to aircaft design - why put in lots of fancy, expensive curves when a flat slab of bl...dy tough glass from the parts bin will do. Some serious windshield heating in that piece of glass - 2 alternators (one backup) needed to provide the juice for windshield heating and prop de-icing.

Take the dimmer for the CWD warning lights on the LET for instance. The Americans would have used a fancy dimmer system with rheostats and photo cells - LET just used a folding smoked perspex cover to dim lights at night. Space pencil approach, but it works and doesn't break.

Rather fly behind a Walter than a PT6; they are bullet proof engines that do not have a fraction of the hot section problems of a PT6, can run on fuels that a PT6 would choke on, and a lot more economically as far as maintenance goes, at that. I figure if you could chop up a PT6 fine enough to fit in the fuel tank the Walter would run on it and spit out the soft bits.

Walter has a slightly higher fuel consumption than PT6A since it uses a slinger ring for fuel distribution instead of fuel nozzles. Then again this prevents hot spots in the hot section.

Never had a moments grief from a Walter and never had a failed start in I guess around 5000 cycles. How many replacement PT6s you looking for again, I am sure you could enlighten us Propspanner???? Walter doesn't even have a hot section inspection between overhauls - doesn't need one.

Guess that's why they re-engine the Thrush with the Walter despite the harsh environment these ag aircraft operate in.

I still reckon that it's time someone came up with a new design in this category of aircraft since the contenders are really thin on the ground - there's got to be a ready market. What other 19 seat twin turbine aircraft are there with STOL capabilities? There's the DO 228 but it 's an expensive aircraft to operate with those Garret engines. Both the Let and the Otter were designed in the 60s and airframe maintenance costs on the Otter are high.

My ideal aircraft in this category would have the following characteritics:

* STOL capabilities
* Simple yet efficient airframe of metal construction and modern design.
* Comfortable, quiet cabin with efficient airconditioning system
* Simple systems
* Light weight with OEW not greater than 35OO kg.
* Ability to carry a payload of at least 2700 kg.
* Cruise speed of at least 180 kts, preferably higher.
* Generous baggage capacity.
* Walter engines.
* Low maintenance and operational costs
* Coffee machine
* Africa proof (OK, maybe that's a bit unrealistic)

Asking a lot isn't it? However, look at how aircraft like the Cirrus SR20/22 have taken a quantum leap in aircraft design by starting with a clean sheet of paper. I reckon a DO228 derivative with Walter engines would come close. Gotta make it look a bit prettier though and something has to be done about that cabin! DO228 has a great wing though.

Let's try and keep this discussion to sensible debate instead of bringing security van discussions into the equation, my opening comments not withstanding!

ps. Why do twin Otter pilots hold handies on take off - is it that scary? I thought that the Otter Guys were really friendly until I realised they weren't waving but holding the power levers!

[Shrike200]

It looks like a flying fidelity gaurd van. Look at the front cocpit windows

Ha Ha! I was wondering if I was the only one who thought that!

[chuks]

If you take a look at an Otter (DHC-3) you will see where that odd power lever arrangement came from. There was just no room anywhere else for the engine controls on the Twin Otter, I think. Like the turn signal switches on modern BMW motorcycles, it works just fine once you get used to it.

I had a spell off flying once, when the last thing I had flown was the Twin Otter. I next found myself in a Cessna 441 simulator, when the instructor and the guy in the right seat were a bit puzzled why I kept grabbing at the ceiling at first when I wanted to make power changes. Just one of those 'bush pilot' habits, I guess they thought.

[maxpwr]

Interesting to read that most who have negative comments about the L410 have never flown one and have very little knowlege about performance and systems.

Not very proffessional....

[Goffel]

:}
Who gives a sh1t about the Fidelity looks.
I just wish I could move my windscreen wiper out of the way so that I could see out of the window.(bit short).

My boss has had our's certified (so he believes and expects us to believe it as well) for 18 pax,2 fat crew members,150kg in the nose,350kg's in the rear and full fuel.

And that does not include the coffee machine.

Oh yes,ours is a UVP,3 blade.

Tells us that if we are not happy flying it,there are plenty of other morons out there that will be more than happy to fly our 'Humping Whale" as he has had it certified.

Where you come with this 10 day maintenance plan.

:mad: Broer.

So if anyone of you claims that the UVP has a payload of 1310kg's, a MTOW of 5800kg's my boss says you are a liar.

And he knows.
(It is just that we are too stupid to know).:E

[wheels up]

Ha,ha,ha.

Unfortunately, I have no doubt you are serious.

Registration 3D-fill in the blanks.

L410UVPSP (Special Performance - I'm sure the performance is something special)

Heres a picture of one of 2 L410UVPs operating in Guinea with L29 droptanks bolted to the wings! STC - what's that??? This is Africa Broer.

http://planes.cz/l410/l410.asp?xml=a_l410&xsl=fotografie_l410&id=czdo31122_3XGDKGALEXBKO84.jpg

[Very_Low_and_Fast]

Any ideas about Skytruck? or PZL M28.

Few companies have started operating with them. Any reports?

"PZL M28 SKYTRUCK - GENERAL DESCRIPTION

DESCRIPTION

The M28 SKYTRUCK Model 05 is a twin-engined high-wing cantilever monoplane of all-metal structure, with twin vertical tails and a robust tricycle non-retractable landing gear, featuring a steerable nose wheel to provide for operation from short, unprepared runways where hot or high altitude conditions may exist. The M28 is best suited for passenger and/or cargo transportation.

GENERAL CHARACTERISTICS
short takeoff & landing (STOL) capability
perfect flight handling at low airspeeds
high useful load, mission versatility
unpaved airstrip operating capability
easy access through rear cargo door, fitted with a hoist for cargo loading and relocation inside the cabin
high-wing arrangement for protection of engines and propellers against damage when operating from unpaved airstrips
easy and quick conversion of the cabin interior configuration
low operating cost
PT6 engines of inverted configuration for efficient protection against foreign object ingression owing to inertial separators installed inside air inlet ducts."

http://www.pzlmielec.pl/ang/fly01.html

[let410fly]

LET 's review the comments posted so far.

Shrike 200
"So, in true rough-field, poorly prepared surface
operations, the Twotter wins hands down"
If this is the case, then why are the L410 displacing
the Otters in Algeria, operating into all the strips
previously serviced by them. It's a case of being the
equal in STOL dept. I've also seen the LET operate in
mud and slush, and its no slouch. Remember this
aircraft was built to be operated by Russians in
Siberia.
As for the gear, nothing beats the trailing link of
the L410, the Otter nose wheel being more suitable on
a wheel barrow as previously noted.
As for the stats regarding fatalities in Africa, why
do you choose to ignore the fact that the LET you
taxied in Algeria, was registered in South Africa, to
western standards. Have there been any accidents in
South African LETs, that are maintained by factory
trained engineers? I could comment on the possible
reason for the accident rate of LETs that fall outside
of the factory control, but there would be howls of
protests about not being politically correct.

Propspanner
Deon, are you still miffed that the LET earned the
moniker "Beechcraft recovery vehicle"?
The cockpit windows, well once more they were
constructed to with stand the 1kg (frozen) chicken
test. Remember Siberia? I know which windshield I
would like to find myself behind when faced with a
vulture, never mind that 1900's windshields have to be
replaced without a bird strike.
As for the Walter, "wheels up" correctly points out
that it is replacing PT6s on other aircraft. The
Walter does not need fancy electric and engine fuel
driven fuel pumps to run, it will start and run on
only the gravity feed from the fuel tank. The FCU can
also be overridden by manual control, something I
think is only available on the C208 PT6.

chuks
The LET is know amongst those who fly her, as a large,
easy going pussy cat with no known vices! The handling
characteristics are akin to a C172. No lurking to bite
you in the arse! Your noise comments say it all in
terms of fuel to noise converter.

wheels up
You've hit the nail on the head, especially when it
comes to the reason why the Otter wing came off when
farming in the sand. As you pointed out, the Walter is
a reliable engine with its only down side the higher
fuel consumption. But maybe this is more preferable to
an engine failure on a fancy PT6 after a bit of rough
handling?
What you perhaps did not elaborate on though, was the
amount of thought that has gone into the design, in
making it a simple, reliable and safe aircraft. For
instant, the gear that is driven into the locked
position on touch down, unlike propspanners 1900, that
collapses in the event of down locks not working.
How about the ergonomically placed power levers, so
that you do not look like a caged chimpanzee on power
changes!
As for the replacement of a LET, as per DC3, another LET!

maxpwr
Full agreement!

Goffel
Could your boss register that machine in any half
decently run country?

Further, the LET is a more comfortable aircraft in the
pax seating department and easier for entry and exit.
The Cargo door makes it more suitable for Medivac
requirements.

Should you require any data on operational costs and
parameters, why not try contacting NAC Lanseria/ Jan
Rehousek/LET factory.

Thanks for the time.

[Robinson Crusoe]

Pilots will always be biased to what they first flew. ( Unless it was the Skyvan), However I truly think the Twotter is the most rugged bush a/c between the two. The only better one is the Buffalo, but that is in a different league.
In a twotter, we landed on an AP mine, assesed the damage, cut the remaining rubber off the rim, took off and flew home. Landed at base, further inspection, fitted a Caribou main wheel and then flew another two weeks waiting for a spare. I doubt that a Let could do that. But "LET's" hear the war stories.

[Solid Rust Twotter]

Chris? That you, boet?

[Robinson Crusoe]

Yebo, who dat?

[maxrated]

Dude, the twotter crash in Algeria may have had more to do with pilot competance or lack thereof, re the runway excursion, than the relative structural integrity of the aircraft.

I have only flown on the let as a pax , far more comfortable than a twotter however it didnt look like half as much fun to fly as the twotter.

Personaly I love having the two big power levers on the roof of the cockpit, it makes me feel like I'm flying a WWII bomber, especially at 50 foot over the Sahara in the late afternoon, (obviously with no pax onboard).

I also noted that the twotters semed to be less maintenance intensive than the let , IMHO

Someone mentioned that twotters are more tricky when it comes to landing in strong crosswinds, well if you have a 35 -40kt crosswind and a 20meter wide runway you can actually land across the runway at 90 degrees straight into the wind, as your landing forward ground speed will only be about 15 knots. (Normal twotter ops in Sudan). Try that with a let ?? or if you have the tundra tyre kit on the Twotter you dont even need to have a runway, just a clear open area.

And finaly just one last completely gratuitous stab at the matter, when AEA replaced the Tegentour Twotter with the Let, they had to bullsh1t the performance A numbers for take off out of REG strip, so that the client , a well known British petrolium company,would accept the Let for the contract.

Unless they extended he runway at REG (which was only 800 meters at the time) theres just no way that the Let complied with Perf A ( the clients requirement) in the middle of an Algerian Sahara'n summer at 50 deg ambient, I recall the lets graphs only went to 35 ambient temps.


Like you said the let was designed for flying in harsh conditions in Siberia possibly not at 55 deg midday temperaturs in the Sahara.

Have a bottle of Algerian Red for me,

Regards Max


:cool:

[wheels up]

What you haven't considered is that after the "runway" at REG there are a couple more kilometers of "runway" before you encounter any obstacles (depending on the runway). In actual fact, the "runway" at REG just consisted of a line of tyres placed on the desert surface; until recently there was no difference in surface between the "runway" and the surrounding desert which is sufficiently hard to support the Let's weight for TO and landing purposes. If there's any place I would rather lose an engine on take off, it would be at REG.

Sometimes the textbook answers that may work in an airline environment need to be tempered with a bit of common sense. Does the "runway" end just because there the line of tyres comes to an end?? Is that thing a "runway" at all????? Ain't easy to spot in a sandstorm, I can assure you.

I think this photo going into REG pretty much sums it up:

http://www.avcom.co.za/images/1124146433photo2.jpg

However, Maxrated, you do touch on an aspect of operating the LET compared to the Twin OTTER. Having a Max TO weight greater than 5700 kg, the LET has to comply with the more stringent requirements of part 121.

I have never flown the Twin Otter so cannot comment on what it's like to fly. What I can say though is the LET is a hoot to fly, with nicely balanced controls and really no handling vices that I have encountered. Personally I prefer flying the L410 to the L420, the L410 having lighter controls with more feedback.

I am often astounded by the short field landing capabilities of the aircraft, not quite matched by the short field TO abilities - you can land in a shorter strip than you can get out of! Short field landing technique consists of hitting full reverse and spoilers on touchdown with firm braking. The spoiler really dump the lift and increase the braking effectiveness. Some captains have been known to apply spoilers just before touchdown (if it looks like its going to be a greaser) to bring an overconfident co-pilot down to earth - literally! The anti-skid significantly shortens the landing distance on a dirt strip - you can feel the brakes "pumping" as the anti skid kicks in and out. Ever tried taking off across that 20m wide runway, Maxrated?!!! Hope you had a nightstop kit.

I reckon the Let will give the OTTER a run for its money in the short landing department, although the OTTER will get out of shorter strips due to its lower Vr. Then again, if you have at least 900 m to meet the Accelerate Stop / Go requirements I would rather have the extra speed and comfort of the LET.

As far as maintenance goes, the LET is a more complex aircraft than the Twin Otter, so obviously the extra systems require additional maintenance. The LET maintenance schedule consists of a series of 10 day inspections followed by a 300 hour, 1200 hr and 4800hr inspection of increasing intensity. The Twin Otter has a couple of ADs out on the airframe (NDT testing of the wing struts for instance and corrosion inspections on the wings) that make it an expensive aircraft to maintain.

As for temperatures, is the Otter certified for operations above 50 degrees? Like any aircraft, you are going to lose performance in the extreme temperatures we have to endure out here - I am sure the Twotter is not a rocket ship when the mercury creaps into the 50s. Then again, water injection giveth back what the heat taketh away....thank God (and LET) for that!

[let410fly]

maxrated

Sand is sand, and both went off the runway about the same distance, yet the LET suffered no consequences!

Once more the Otter operators are using the old tired and worn out smoke screen of claiming that the LET does not operate in high ambient temperatures. Then why the water injection, which is not available on the Otter, but is on the LET?

As for REG, I have been informed that the runways remain unchanged from your days, and the let has no problem operating out of there. Sour grapes perhaps?

I have seen the LET POH, and the graphs are for 50 C ambient, which is higher than the Otter, so that scuttles the argument that the LET is only good for cold climates!

As the LET is greater than 5,700 kg, a proven single engine climb performance is a certification requirement. The Otter, however, at 12,500 lb, is only required to show that it can take off, no requirement to prove what it can do after an engine failure.

The plus side to the LET 420 at TEG, is that it has the ability to operate into all the strips serviced by the Otter and has the range to perform a Medivac to Gaurdia and Hassi Messaoud, which it has done.

Would seem to me that the LET leaves the Otter in the dust in all aspects, and as is happening, will continue displace the Otter where the two are now going head to head.

[V1... Ooops]

I cannot comment on the LET, never having flown one, but I can comment with some authority on the Twin Otter, having written the book on the aircraft (the FlightSafety Training Manual & Checklist), spent 5,000+ hours training Twin Otter pilots, and having considerable experience flying them in a variety of places, Hassi included.

First, a few statistical corrections to earlier posts: There were 844 Twin Otters built, the production run was as follows:

- 6 pre-production prototypes, model designation DHC6 Series 1 (2 of which are still flying, one in service with NASA).
- 109 Series 100 aircraft, which was the first production run. (The total of 115 given earlier includes the 6 Series 1 aircraft). Most of the few remaining Series 100 aircraft still flying are used for recreational parachute dropping.
- 115 Series 200 aircraft.
The balance (SN 231 to 844) were Series 300 or derivatives. Slightly less than 600 remain in service today. Series 300 have a MTOW of 12,500 lbs, the earlier series are limited to 11,596 lbs MTOW.

Concerning the derivatives built during the production run – series 110, 210, and 310 conformed with UK certification regulations (minor electrical differences, mostly), and Series 320 conformed with Australian certification regulations (minor avionics differences). 310 and 320 Series aircraft can be operated as if they were 300 Series, in accordance with the 300 series AFM, if so desired, provided the regulatory authority does not require conformance with UK or Australian regulations.

The two ‘Killer’ Twin Otters made – the 300M series – were both sold to Senegal for coastal fisheries patrol. As with the 310 and 320, they were part of the regular Series 300 production, modified as needed. One has since been returned to civilian use as a Series 300 aircraft. There were also a small number of Series 300 aircraft that were fitted with enhanced avionics, wing spoilers, dual zone engine fire detection, anti-skid, and an electrical system that conformed with FAR 25 for a STOL air carrier demonstration project in Canada. These were eventually sold to Transport Canada for utility use, and all were converted back to the 300 spec. Transport Canada has since sold these, they are out in the civilian world now.

The Canadian Military purchased some DHC-6 300 aircraft for utility use, and assigned them their internal reference number CC-138. They are nothing more than normal series 300 aircraft with slight modifications as requested by the customer – a roll-up door, bubble windows for SAR use, and so forth. The United States Air Force purchased 2 series 300 for parachute dropping – they still operate them, and designate them as the UV 18.

All the aircraft described in the above two paragraphs conform to the civilian type certificate for the DHC6 300, the differences requested by the customers having been incorporated by way of engineering orders only.

--------------------------------------------

In 1998, I made a study of all DHC-6 accidents and incidents from 1965 to 1997 – about 600 events in total. It is interesting to observe the ranking of accidents by type and accidents by causal factor (classified by ICAO standards).

The 5 leading accident causes by type for that time period were:

1) Loss of Control - Ground or Water (69)
- during takeoff or landing phase, about an equal split
- unsuitable terrain the most common factor
2) Collision with Rising Terrain (59)
- CFIT, almost always multiple fatalities
- pressing the weather, VFR flight to IMC destination
3) Collision with Objects (54)
- during taxi, takeoff or landing
- includes 30 accidents related to hydraulic CB pulled
4) Heavy Landing (48)
- often includes stalls, attempts at STOL landings
5) Collision with Ground or Water (31)
- hit the ground or water during approach.

The top 5 causal factors – for the same group of accidents – were:

1) Continued VFR flight into deteriorating weather (52)
- Pre 1990 - CFIT enroute to destination
- Post 1990 - CFIT near destination after GPS navigation enroute
2) Unsuitable terrain (34)
- inadequate runway surface
3) Misjudgment of distance (34)
- undershoots and overshoots
- hitting trees on approach or takeoff
4) Improper landing technique (23)
- stalls, or carrying power into the flare to try and get a “greaser”
- props not forward prior to landing
5) Failure to compensate for wind (22)
- landing or takeoffs in thunderstorms, crosswinds too great
- groundloops (!)
- blown off runway into trees, ditches, etc
- short runways and strong crosswinds at the same time.

I think it is fairly clear that the bulk of DHC-6 accidents arise from attempting to operate the aircraft in an environment that is simply not suitable for an aircraft – any aircraft. I don’t think there have been many Boeing, Airbus, or Gulfstream aircraft damaged as a result of ‘Takeoff or landing attempted on unsuitable terrain’ or ‘blown off runway into ditch’.

Accident rates for the DHC-6 have declined sharply since the mid 1990s. One of the reasons for this is the introduction of the DHC-6 simulator in Toronto in the early 1990s. A second reason is the general tightening up, worldwide, of supervision of remote and utility operations by either clients or the regulatory authorities. The bulk of accidents that have taken place since the late 1990s can be attributed to pilots not following the procedures published in the AFM – pilots pulling circuit breakers, or not using full calculated power for takeoff, or landing with the props in the minimum governing position. There have only been 2 DHC-6 accidents over the past 40 years attributed to mechanical failure of otherwise properly maintained aircraft.

‘let410fly’ makes reference to performance calculations and data relating to single engine flight. There are two different sets of certification data available for use with the DHC-6 300 series. One is the original CAR 3 data, the other is the SFAR 23 certification data, which was published after the aircraft had been in service for some time. The SFAR 23 data does provide all that is needed to make a well informed decision about runway length required for accelerate-stop and single engine climb performance following V1. That data can be found in Supplement 11 of the AFM. The operator has a choice of using either the CAR 3 data, or the SFAR 23 data, to govern their operations. Most operators now choose to use the more conservative SFAR 23 data.

With respect to the Twin Otter being a 'handful' in heavy crosswinds, keep in mind that the stalling speed of the aircraft in the landing configuration can be as low as 50 to 55 knots. If you have a 25 knot crosswind, that's a 50% crosswind component. I am sure that a Boeing with a stalling speed of 120 knots in the landing configuration would also be quite a handful in a 60 knot crosswind - the same percentage. The low stalling speed gives the Twin Otter unique advantages, but as pilots, we have to remember that the aircraft reacts to the crosswind component, not the crosswind in knots.

As I mentioned at the beginning of this post, I have no knowledge about the LET, and for that reason, I cannot comment on it or draw any comparisons.

Michael

[wheels up]

Interesting post V1.

As usual the majority of accidents caused by the nut on the end of the contol yoke.

[let410fly]

V1... Ooops
Thank you for a very informative reply.

I trust that this now puts the argument about legitimate LETs and the other cowboys in the right perspective. LET's not hear the trotting out and dusting off of old worn-out cliché’s, untruths and downright lies, as espoused by the Otter drivers every time the LET is mentioned.

Soap Box Cowboy
Thanks for the topic................... see you in Hyde Park?
Cheers

[V1... Ooops]

I posted some additional information related to the history of Twin Otter accidents on this post, in response to a question that was raised there: http://www.pprune.org/forums/showthread.php?s=&threadid=186105

[let410fly]

Looks like Otter driversput tail between legs and fled.

So, Otter superior aircraft,Myth.......................busted!!!!!

[Solid Rust Twotter]

Nope!

Just couldn't be bothered responding to your uninformed drivel.....

[308]

There's only one plane that can replace a Twotter,,,- another Twotter, sava!

[V1... Ooops]

I understand that the LET is available with two different engines on it - the original fitment, and a PWC engine. Is there a significant difference in performance - in particular, single engine performance - between the two? Did the manufacturer publish different performance data (takeoff run, rate of climb, SE climb, etc.) for the PWC engine when it was offered later on?

Michael