Twin Otter Beta Use in Flight

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pelmet
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Twin Otter Beta Use in Flight

Post by pelmet »

I recently met a pilot who used to fly in Nepal. He was quite interesting and had flown Twin Otters. Along with his flying experiences, we discussed some of the accidents that had happened there as well as some of the interesting airstrips that he had flown to includin Lukla, a famous one for Youtube videos.

He mentioned something that I had never heard of before. He said that they had approval to use Beta in flight. He said that they do not go all the way into full reverse but they do bring the power levers aft of the idle stop which gives them a high rate of descent for very steep approaches.

This surprised me as I had been told to never do such a thing and was under the impression that actual flight control could be lost due to interruption of airflow over the tail. Has anyone ever heard of this kind of approval?
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Re: Twin Otter Beta Use in Flight

Post by PilotDAR »

Use of Beta in flight is prohibited in 2.4.1.1(11) of the -400 POH, engine operating limitations table footnotes. I'm sure its prohibited in the -300 and earlier POH as well. So, unless they had a different POH approved with this limitation removed, which would be an immense program, or, they were somehow exempt from it, such operation is prohibited.

If you're flying a Twin Otter into a runway whose surrounding terrain is so steep that you need to be in beta range to get in, you're probably never going to get it out. Such operation is not necessary in a Twin Otter. Yes, pitch control becomes very spongy if you select beta in flight. deHavilland aircraft have crashed as a result of the misuse of beta in flight.
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Bronco Billy
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Re: Twin Otter Beta Use in Flight

Post by Bronco Billy »

We have lots of experience pilots on offstrip operations. Many strips are no longer then 600-800 ft. None of them use beta before landing to get in. It is in my opinion a bad and unsafe practice. Good thing to know thats all.

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Re: Twin Otter Beta Use in Flight

Post by valleyboy »

I have heard of people using "beta" decent after dropping sky divers - never thought it was smart but some had the big cahonies -- the porter on the other hand beta was used a lot for approaches and decent.
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Re: Twin Otter Beta Use in Flight

Post by PilotDAR »

One of my many mentors trained me in Twin Otters, and he really knew what he was doing in that plane. We were approaching Cairo during a ferry flight, he flying, me on the radio. We were very close to the airport, cleared overhead to join a long traffic pattern, at 6000 feet. Unexpectedly, the controller said to me: "PH-STE, I have a break in traffic, if you can be down and clear of the runway in two minutes, you're cleared to land now.". I asked my mentor if we could accept that clearance. With only a moment delay, I saw the power levers smoothly brought back, the nose stuffed way down, and he said: "yes". We were down and clear within the two minute allowance - smooth art of flying, not a bump. My only view of the horizon on the way down was out the side windows, the windshield was filled with airport and desert. As we taxied in, he said to me: "I don't want to see you trying that.".
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golden hawk
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Re: Twin Otter Beta Use in Flight

Post by golden hawk »

It's been years, but.....as I recall on the Twin Otter, 'beta range' is when the propeller rpm is controlled by the power levers, not the propeller levers (a blade angle of less than 17 degrees).

With power levers idle, blade angle won't go less than 11 degrees unless you twist the grips. This disables the beta back up valve, so you can retard the power levers further to achieve a blade angle less than 9 degrees to -15 degrees.....AFTER TOUCHDOWN.

"Beta range" happens on every approach made; 'in flight beta' has always been there. The aircraft was engineered this way to improve short field landing performance.

Twisting the grips and further retarding the power levers simply deceases the blade angle further., reducing the landing roll. It was NOT intended to be used in flight, and was never tested for in flight use.
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NWONT
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Re: Twin Otter Beta Use in Flight

Post by NWONT »

I flew for Windward on St Maarten in 1990. This was standard procedure on Saba and St Barts. I don't know if it was approved or in the SOP's. If we had SOP's I never saw them. I'm sure it's done many other places.
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ahramin
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Re: Twin Otter Beta Use in Flight

Post by ahramin »

So to sum it up, it is not allowed, it can be done, it is done, and it has been the direct cause of several accidents.

Draw your own conclusions ...
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Re: Twin Otter Beta Use in Flight

Post by AuxBatOn »

So, instead of saying "no" when something cannot be done within the sandbox given to a pilot (within what is in the AFM and regulations), pilots will just, off the cuff, execute expressely prohibited maneuvers without proper airworthiness authority?

We want to be called "Professionnals" but we can't do simple things such as follow aircraft manuals and rules...

Busting an SOP is one thing. Busting limitations is another, much more serious one.
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Re: Twin Otter Beta Use in Flight

Post by NWONT »

Not sure why I get into these discussions...bored I guess. Flight-Safety trains in the safest possible flying techniques. They train with lawyers in mind. If they could make a rule that you need 10,000 ft of paved runway to fly a twin otter...they would. What could possibly go wrong if this was the limitation? I've been retired for some time but one way they teach is if you have a steady beta light you are to power back, feather the prop pull the breaker....then bring it back. So much easier to just twist the grip if you need a few extra seconds to find the breaker. They said it was because some fool did something wrong so they had to make it fool proof!!!....OK, roger on that!!! The MNR often pushes the limits to get the job done...like off-strip work. I'm not going to go into it but Flight-safety won't instruct for these procedures so we took our own guy and just rented the sim for this training.....or, I guess we could just say off-strip work just isn't safe so we aren't going to do it!!!
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SuperchargedRS
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Re: Twin Otter Beta Use in Flight

Post by SuperchargedRS »

AuxBatOn wrote: Sun Feb 11, 2018 12:11 pm So, instead of saying "no" when something cannot be done within the sandbox given to a pilot (within what is in the AFM and regulations), pilots will just, off the cuff, execute expressely prohibited maneuvers without proper airworthiness authority?

We want to be called "Professionnals" but we can't do simple things such as follow aircraft manuals and rules...


Busting an SOP is one thing. Busting limitations is another, much more serious one.
More aviation industry self flagellation :roll:

Also I am a professional... based on the webster definition, frankly I don't care what you call me, as long as it's not Shirly, labels and medals and rank are for the mouth breathers, I care about my quality of life, call me whatever you want, I'll still protect the skin, tin and ticket and keep on showing up for work as long as the paycheck is big enough and keeps on clearing.


Guess what, the same can be said for about every industry, ever wonder why docs often have malpractice insurance, or why more every professional trade has some type of F' up insurance required.


Back to the topic, Ive heard of people (not twotter pilots) putting a PT6 into ground idle before landing, but the beta stuff I've only heard that "trick" from drop zone pilots, out side from the legality, it's not something I'd do, for me the risks would outweigh any rewards IMHO.
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C.W.E.
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Re: Twin Otter Beta Use in Flight

Post by C.W.E. »

The Twin Otter needs Garrets and then you could really get down in flight idle.

And you would solve the Beta problem.
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Re: Twin Otter Beta Use in Flight

Post by Heliian »

NWONT wrote: Sun Feb 11, 2018 10:43 am I flew for Windward on St Maarten in 1990. This was standard procedure on Saba and St Barts. I don't know if it was approved or in the SOP's. If we had SOP's I never saw them. I'm sure it's done many other places.
It used to be done, nothing written.

Until they twisted one in in st.barts and killed a bunch of people.

It's been reinforced many times to not do this. Don't do It, no matter how good you think you are. Period.
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Re: Twin Otter Beta Use in Flight

Post by PilotDAR »

We consider limitations carefully when drafting the wording of flight manuals, and flight manual supplements. Pilots of certified aircraft expect that aircraft to be safe, with predicable flying characteristics, not requiring unusual pilot skill or attention. That's what you get if you follow the flight manual. Would you like to be a test pilot? That's a different job, with a lot of its own rules, and surprises.

While flight testing the 182 amphibian, I selected reverse during a landing, while I was still on the step. There was no FMS for that prop on that airplane, and the FMS for that prop on other seaplanes made no mention of "don't do that". My choice to do this was poor, and I instantly had to apply lots of extra skill to keep the plane going forward and upright. So, the FMS for that aircraft, with that propeller, states not to select reverse while on the step. I have expressed it as a limitation. A pilot has no choice but to adhere to it to operate legally. If someone would like to have the limitation removed, they can undertake an STC program to do it.

In the mean time, if you even wonder if you should follow limitations - you should.
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Re: Twin Otter Beta Use in Flight

Post by C.W.E. »

In the mean time, if you even wonder if you should follow limitations - you should.
Laws, rules and aircraft operating limitations are put in place for the safety of people.

Not following them can and most likely will end up getting you into unnecessary grief.

Real professional skilled pilots follow these laws, rules and limitations.
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dogfood
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Re: Twin Otter Beta Use in Flight

Post by dogfood »

Pc12 we had to do it sometimes on the short strips wasn't really a big deal yeah the afm says not do it but when the alternative is going off the runway. I know what I'll pick
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Re: Twin Otter Beta Use in Flight

Post by SuperchargedRS »

You had to go into beta range, wheels down, 40 flaps, in a PC12??

What the heck were you landing on?
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Re: Twin Otter Beta Use in Flight

Post by dogfood »

1000foot unprepared mine camp strips
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Re: Twin Otter Beta Use in Flight

Post by SuperchargedRS »

What was your weight on landing?
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Re: Twin Otter Beta Use in Flight

Post by golden hawk »

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