V1 in small twins

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digits_
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V1 in small twins

Post by digits_ »

Most, if not all, operators that fly twin engine aircraft, use V1 as the decision speed for small twins. An engine blows up before V1, you abort, an engine blows up after V1, you continue and rotate. Ok, great.

Now, V1 makes a lot of sense if you look at airline operations. It truly is a decision speed. Reduced power take offs, runway conditions etc are all taken into account to be able to say with a certain degree of precision that if you try to abort above V1, you'll slide off the end of the runway. If you continue single engine before V1, you'll hit someting at the end of the runway. This makes sense. V1 has value. You can trust it. It's well defined.

Looking at smaller operators flying twins, they also use V1. For small jets, for twin turbines, even for piston twins. I find the values and meaning of those V1 speeds often pretty useless, and in a way pretty detrimental to safety.

Let's start with an example of a navajo. Accelerate stop somewhere around 3000 ft, single engine stake off distance probably around the same. This airplane is now taking off from a 10000 ft runway, with a V1 calculated for a 3000 ft runway. You have 7000 ft of extra runway that is not taken into account. Let's say its engine catches fire past v1, would it not be much safer to just abort in the remaining extra 7000 ft? On such runways, why would V1 ever be lower than Vr?

Same for a king air class kind of airplane. They are great performers. Why treat V1 as a life and death decision on a long runway? If you have 10 000 ft and something happens, even past v1, why not abort?

It just drives me bonkers. Discussing it with management or training pilots, even crew members always results in "But it's V1, it's the decision speed, you can't abort past V1!".

Thoughts? Am I missing something?
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172_Captain
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Re: V1 in small twins

Post by 172_Captain »

I fly a small twin turbine medivac and often fly into 3500 gravel strips. My briefing is usually the same regardless of runway length however. Anything prior to 80 knots we’ll reject. Between 80 and rotate, were only stopping for an engine failure OR a valid fire. I’m not stopping at 95 knots for a gen failure, and I’m not attempting to go airborne with a dead engine off a reserve in a plane that doesn’t have a demonstrated Vmcg speed, or any guarantee that it will become airborne or climb away before the trees at the end of the runway.
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Re: V1 in small twins

Post by jschnurr »

http://www.kingairmagazine.com/article/ ... -rotation/

tl;dr Gear up is your decision speed. Exact time depends on many factors.
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pelmet
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Re: V1 in small twins

Post by pelmet »

Small twins don't have a V1, at least nothing official.

By coincidence, I am just finishing up a fairly large accident report on a King Air 90 crash in Australia. There is some good info in it.....

https://www.atsb.gov.au/media/24353/aai ... 18_001.pdf

I suggest starting at part 1.20.4 as well as 2.4.1 for information on the subject.
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airway
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Re: V1 in small twins

Post by airway »

Another thing to think about if you choose to land after lift off is the flap setting. The recommended or approved flap setting for take off can be very different from the landing flap setting. The stall angle of attack in the flare may also be very different than what you are used to.
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Re: V1 in small twins

Post by airway »

Oh, and you might be in an overweight landing situation then as well.






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AuxBatOn
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Re: V1 in small twins

Post by AuxBatOn »

There are two speed to be aware of when talking about rejected takeoff (in a multi-engine aircraft).

First is what my community calls the minimum go speed. That's the speed at which if an engine fails, a takeoff can still be accomplished.
The second is the maximum abort speed. That's the speed at which you can initiate an abort and stop on the remaining runway.

Transport Canada's definition of V1 is left to the operator. In the AIM, TC defines V1 as the "critical engine failure recognition speed" and notes that "This definition is not restrictive. An operator may adopt any other definition outlined in the aircraft flight manual (AFM) of TC type-approved aircraft as long as such definition does not compromise operational safety of the aircraft."

So, in practical terms, V1 can be anywhere between the minimum go/no-go speed and the maximum abort speed. Regardless of definition, the important part is to have those gates in your brain:

1- The speed before which a rejected takeoff will be performed if an engine failure occurs (that speed needs to be equal to or greater than the minimum go speed); and
2- The speed at which a continued takeoff will be performed if an engine failure occurs (that speed needs to be equal to or less than the maximum abort speed).

Those speeds could be the same and that's not an issue.

A note of bringing an aircraft down after takeoff. Unless there are over-riding factors, the airplane should be able to fly on one engine after takeoff. I would be cautious of bringing the aircraft down after takeoff unless one is 100% sure it can be brought down safely within the remaining distance. When that's part of my emergency plan, I normally use runway markers as a "gate" to bring it back down (ie: past the 4-board, we keep flying). I would consider more than the normal landing distance over a 50 ft obstacle (ie: give yourself some pad) to account for the dynamic nature of the manoeuvre and the fact the manoeuvre has most likely never been practiced.
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Last edited by AuxBatOn on Thu Nov 12, 2020 8:22 pm, edited 1 time in total.
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Re: V1 in small twins

Post by photofly »

In case anyone is finding this topic for the first time, this is an interesting read:
https://www.gofir.com/aviation_accident ... safety.pdf
We'll use a Cessna 421 for this exercise and remind you again that we're not picking on the 421. It's just that Cessna is honest enough to try to tell it like it is in its owners manuals.

...

Let's get some real-life factors into the single-engine takeoff equation. Suppose, as is usually the case, we begin the takeoff roll about 75 feet from the approach end of the runway and do so without holding the brakes. This could add 475 feet to the handbook figure. Next, suppose we lose the engine at rotation, but it takes us three seconds to recognize the situation and react. (This, by the way, is a very conservative figure.) The reaction time will cost us about 537 feet. Now the total horizontal distance from the beginning of the runway to a point at which the aircraft is 50 feet above the surface (assuming engine loss at rotation) is 6,012 feet, an increase of 20 percent. The 421's sea-level, single-engine climb rate is about 305 fpm. Assuming that we want to get at least 500 feet under us before trying anything fancy like returning for a landing, we must continue more or less straight ahead for one minute and 28 seconds. This climb will cover a horizontal distance of some 16,485 feet bringing the total distance covered from the rotation point to 19,485 feet, or 3.7 miles.

If all this happens at a sea-level airport on a hot day (ISA plus 20 degrees C.), we will not reach the 50-foot level until the aircraft has covered a horizontal distance of 7,040 feet from the point of rotation and engine failure. ...

You might be able to live with that 10.6-mile hot-day figure on a departure from JFK where you could head out over the Atlantic, but the same departure from Teterboro would make collision with obstacles almost a certainty.
Oh, and so is this:

https://www.pittspecials.com/articles/MultiTakeoff.htm
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Last edited by photofly on Thu Nov 12, 2020 3:06 pm, edited 1 time in total.
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Re: V1 in small twins

Post by Eric Janson »

digits_ wrote: Thu Nov 12, 2020 8:33 am If you continue single engine before V1, you'll hit something at the end of the runway. This makes sense. V1 has value. You can trust it. It's well defined.
Training on large jets is now to be "go minded" approaching V1.

Because V1 is so critical it is considered safer to continue if something fails a few knots before V1. In this case you will no longer have the 35' obstacle clearance - but you will still clear the obstacles.

When we do a wet runway take-off the 35' obstacle clearance is reduced to 15'.

I don't recall V1 being published for any of the light twins I have flown. There is a grey area between Vmc and Blue line speed - you may or may not be able fly away with an engine failure.

In some cases you may have no option but to treat it like a single engine aircraft - close the throttles and land straight ahead.
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cncpc
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Re: V1 in small twins

Post by cncpc »

If I remember correctly, isn't the calculation for the abort at the blueline in a piston twin? With the blueline being set at Vmc plus 7 knots.
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Re: V1 in small twins

Post by pelmet »

One shouldn't even use the term V1 for the type of aircraft the OP stated. There is no V1 for a Navajo, or smaller King Air's.
AuxBatOn wrote: Thu Nov 12, 2020 2:41 pm A note of bringing an aircraft down once airborne. Unless there are over-riding factors, the airplane should be able to fly on one engine after takeoff.
As a blanket statement, this is definitely incorrect.
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AuxBatOn
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Re: V1 in small twins

Post by AuxBatOn »

pelmet wrote: Thu Nov 12, 2020 6:55 pm One shouldn't even use the term V1 for the type of aircraft the OP stated. There is no V1 for a Navajo, or smaller King Air's.
AuxBatOn wrote: Thu Nov 12, 2020 2:41 pm A note of bringing an aircraft down once airborne. Unless there are over-riding factors, the airplane should be able to fly on one engine after takeoff.
As a blanket statement, this is definitely incorrect.
Pelmet,

The airplane is certified to fly on one engine and it is even taught on the multi-engine rating.

There are no charts for determining the landing distance of an airplane shortly after an engine failure. There is no training to land, in a multi, after an engine failure during the takeoff phase.

You will really say that recommending using the procedure that is taught, certified and flight tested is wrong?

I didn’t say there are no circumstances when this should be attempted - I did provide a caveat (and provided a technique for doing so). But, it should be the rare exception for very specific scenarios, not the norm.

Edit: To provide clarity, here's some examples when you should put it back on: Haven't reached the best angle of climb speed with one engine out (in a small twin), failed engine's prop does not feather, catastrophic event that would jeopardize the ability of the plan to stay airborne.
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Last edited by AuxBatOn on Thu Nov 12, 2020 7:52 pm, edited 1 time in total.
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pelmet
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Re: V1 in small twins

Post by pelmet »

AuxBatOn wrote: Thu Nov 12, 2020 7:25 pm
pelmet wrote: Thu Nov 12, 2020 6:55 pm One shouldn't even use the term V1 for the type of aircraft the OP stated. There is no V1 for a Navajo, or smaller King Air's.
AuxBatOn wrote: Thu Nov 12, 2020 2:41 pm A note of bringing an aircraft down once airborne. Unless there are over-riding factors, the airplane should be able to fly on one engine after takeoff.
As a blanket statement, this is definitely incorrect.
Pelmet,

The airplane is certified to fly on one engine and it is even taught on the multi-engine rating.

There are no charts for determining the landing distance of an airplane shortly after an engine failure. There is no training to land, in a multi, after an engine failure during the takeoff phase.

You will really say that recommending using the procedure that is taught, certified and flight tested is wrong?

I didn’t say there are no circumstances when this should be attempted - I did provide a caveat (and provided a technique for doing so). But, it should be the rare exception for very specific scenarios, not the norm.
As far as I am concerned, airborne means as soon as there is no contact between the aircraft and the ground. Do you really think that many of these light trainers will be able to 'fly' after getting airborne. What does 'fly' mean? Be able to remain airborne. In Calgary, Edmonton, Toronto on a hot day at max weight or close to it. I think not.

This is a discussion about losing an engine at V1 or whatever equivalent there might be for a light twin, not whether the aircraft can fly on one engine loss in cruise or higher altitude situations used in multi-engine rating scenarios.
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digits_
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Re: V1 in small twins

Post by digits_ »

pelmet wrote: Thu Nov 12, 2020 6:55 pm One shouldn't even use the term V1 for the type of aircraft the OP stated. There is no V1 for a Navajo, or smaller King Air's.
Isn't the limit for V1 definition the 12500 lbs? My remarks were also about king airs certified for weights over 12500 and even for small jets such as learjets which have V1 calculations in their FMS systems. Even those airplanes ignore a 10 000 ft runway and calculate v1 based on the runway distance they need. You should be able to abort 20 kts above V1 solely looking at the remaining runway, but even asking or mentioning this was a big no no. Really curious why. Sounds like more people here have more practical mindset.
pelmet wrote: Thu Nov 12, 2020 6:55 pm
AuxBatOn wrote: Thu Nov 12, 2020 2:41 pm A note of bringing an aircraft down once airborne. Unless there are over-riding factors, the airplane should be able to fly on one engine after takeoff.
As a blanket statement, this is definitely incorrect.
I agree with pelmet here. Most small piston twins are not certified to be able to handle an engine failure on the ground. Sure, we train for it, but there is no design requirement for them to be able to get airborne, or to maintain altitude with gear and/or flaps down.
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Re: V1 in small twins

Post by Big Pistons Forever »

There is no certification requirement for a light twin to have positive performance for the EFATO scenario. This is why no V1 speed is promulgated for light twins because a V1 speed by definition requires that the aircraft can continue the takeoff after an engine failure at or above V1.

Sadly there are many examples of smoking holes next to the runway when pilots asked for more than the aircraft was capable after the engine failed right after liftoff

Personally I use gear selected up and blue line plus 5kts as decision gate. Below that if the engine fails the automatic response is to pull back both throttles and I will take my lumps straight ahead. After that I have the option to identify and feather and continue
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Last edited by Big Pistons Forever on Thu Nov 12, 2020 8:07 pm, edited 1 time in total.
AuxBatOn
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Re: V1 in small twins

Post by AuxBatOn »

pelmet wrote: Thu Nov 12, 2020 7:50 pm
AuxBatOn wrote: Thu Nov 12, 2020 7:25 pm
pelmet wrote: Thu Nov 12, 2020 6:55 pm One shouldn't even use the term V1 for the type of aircraft the OP stated. There is no V1 for a Navajo, or smaller King Air's.



As a blanket statement, this is definitely incorrect.
Pelmet,

The airplane is certified to fly on one engine and it is even taught on the multi-engine rating.

There are no charts for determining the landing distance of an airplane shortly after an engine failure. There is no training to land, in a multi, after an engine failure during the takeoff phase.

You will really say that recommending using the procedure that is taught, certified and flight tested is wrong?

I didn’t say there are no circumstances when this should be attempted - I did provide a caveat (and provided a technique for doing so). But, it should be the rare exception for very specific scenarios, not the norm.
As far as I am concerned, airborne means as soon as there is no contact between the aircraft and the ground. Do you really think that many of these light trainers will be able to 'fly' after getting airborne. What does 'fly' mean? Be able to remain airborne. In Calgary, Edmonton, Toronto on a hot day at max weight or close to it. I think not.

This is a discussion about losing an engine at V1 or whatever equivalent there might be for a light twin, not whether the aircraft can fly on one engine loss in cruise or higher altitude situations used in multi-engine rating scenarios.
An airplane needs to demonstrate a couple of things to pass certification. A positive climb gradient (of varying gradient depending on the MTOW and type of engines) is one of those things (gear/flaps up/prop feathered) up to 5,000 ft pressure altitude. Of course, if you haven't reached a safe climbing speed, you may not be able to climb. If your aircraft is capable of flying however, I would argue that putting it back down is not a good idea. It is dynamic and it is something that is not trained to (although the training guide does talk about rejecting takeoff up to Vyse).

Putting it back down should only be attempted if the airplane won't fly (those conditions must be known before power is applied for takeoff), will hit something due to the reduced climb gradient (anothing thing that should be known before takeoff) or if the integrity of the aircraft is compromised (that decision will be made when it happens. For example: explosion on board - yes, it happened).

The bottom line is know your aircraft and know when it can fly. If it can safely fly, I will always take it flying and deal with it airborne. And engine failure should not automatically trigger an airborne abort.
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AuxBatOn
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Re: V1 in small twins

Post by AuxBatOn »

digits_ wrote: Thu Nov 12, 2020 7:58 pm I agree with pelmet here. Most small piston twins are not certified to be able to handle an engine failure on the ground. Sure, we train for it, but there is no design requirement for them to be able to get airborne, or to maintain altitude with gear and/or flaps down.
Takeoff for me is defined until you reach 35 feet. That is how I define takeoff.

FWIW, there is no requirement, in Part 23, to demonstrate a positive climb gradient with the flaps down (and gear down for some types) at all for any weight/engine categories during a transition to a failed engine. The climb/descent gradients just need to be demonstrated through flight test.

There is no formal definition of "small" twin but "light twin" is informally defined as MTOW 6,000 lb or less (this is the cutoff in the certification standards).
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Last edited by AuxBatOn on Thu Nov 12, 2020 10:00 pm, edited 1 time in total.
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Big Pistons Forever
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Re: V1 in small twins

Post by Big Pistons Forever »

At 36 feet the gear will still be down and the speed below blue line. A light twin will not be able to maintain height while retracting the gear and feathering the prop and accelerate to blue line. The reality is these light twins need both engines to achieve positive performance in most scenarios involving a power loss right after lift off.

The old saw about the second engine only going to take you to the scene of the accident is based on the accident record for light twins
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Re: V1 in small twins

Post by pelmet »

AuxBatOn wrote: Thu Nov 12, 2020 8:06 pm
pelmet wrote: Thu Nov 12, 2020 7:50 pm
AuxBatOn wrote: Thu Nov 12, 2020 7:25 pm

Pelmet,

The airplane is certified to fly on one engine and it is even taught on the multi-engine rating.

There are no charts for determining the landing distance of an airplane shortly after an engine failure. There is no training to land, in a multi, after an engine failure during the takeoff phase.

You will really say that recommending using the procedure that is taught, certified and flight tested is wrong?

I didn’t say there are no circumstances when this should be attempted - I did provide a caveat (and provided a technique for doing so). But, it should be the rare exception for very specific scenarios, not the norm.
As far as I am concerned, airborne means as soon as there is no contact between the aircraft and the ground. Do you really think that many of these light trainers will be able to 'fly' after getting airborne. What does 'fly' mean? Be able to remain airborne. In Calgary, Edmonton, Toronto on a hot day at max weight or close to it. I think not.

This is a discussion about losing an engine at V1 or whatever equivalent there might be for a light twin, not whether the aircraft can fly on one engine loss in cruise or higher altitude situations used in multi-engine rating scenarios.
An airplane needs to demonstrate a couple of things to pass certification. A positive climb gradient (of varying gradient depending on the MTOW and type of engines) is one of those things (gear/flaps up/prop feathered) up to 5,000 ft pressure altitude. Of course, if you haven't reached a safe climbing speed, you may not be able to climb. If your aircraft is capable of flying however, I would argue that putting it back down is not a good idea. It is dynamic and it is something that is not trained to (although the training guide does talk about rejecting takeoff up to Vyse).
The current 14 CFR part 23 single-engine climb performance
requirements for reciprocating engine-powered multiengine
airplanes are as follows.
• More than 6,000 pounds maximum weight and/or
VSO more than 61 knots: the single-engine rate of
climb in feet per minute (fpm) at 5,000 feet mean
sea level (MSL) must be equal to at least .027 VSO 2.
For airplanes type certificated February 4, 1991, or
thereafter, the climb requirement is expressed in terms
of a climb gradient, 1.5 percent. The climb gradient
is not a direct equivalent of the .027 VSO 2 formula.
Do not confuse the date of type certification with the
airplane’s model year. The type certification basis of
many multiengine airplanes dates back to the Civil
Aviation Regulations (CAR) 3.
• 6,000 pounds or less maximum weight and VSO
61 knots or less: the single-engine rate of climb at
5,000 feet MSL must simply be determined. The rate
of climb could be a negative number. There is no
requirement for a single-engine positive rate of climb
at 5,000 feet or any other altitude. For light-twins
type certificated February 4, 1991, or thereafter, the
single-engine climb gradient (positive or negative) is
simply determined.


An aircraft less than 6000lbs MTOW(which includes almost all light twins) is not required to be able to climb.
AuxBatOn wrote: Thu Nov 12, 2020 2:41 pm A note of bringing an aircraft down after takeoff. Unless there are over-riding factors, the airplane should be able to fly on one engine after takeoff.
Once again, I disagree with this as a blanket statement. It may apply to some larger twins.
AuxBatOn wrote: Thu Nov 12, 2020 8:16 pm Takeoff for me is defined until you reach 35 feet. That is how I define takeoff.
That comes from Part 25 aircraft(over 12,500 lbs. And certainly wasn't stated in the earlier post. Be prepared to close the throttle and land on the terrain ahead with an engine failure in a light twin soon after getting airborne, including at 35 feet. And almost certainly plan to fly level initially at the engine failure altitude unless quite light at low density altitudes.
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Re: V1 in small twins

Post by Big Pistons Forever »

From the Piper Seminole POH, Emergency Procedures , Engine Failure After Takeoff

“In certain combinations of aircraft weight, configuration, ambient conditions and speed, negative climb performance may result. Refer to One Engine Inoperative Climb Performance chart,”

I am with Pelmet. Procedures for large aircraft which have demonstrated capabilities to continue a takeoff after an engine failure should not be extrapolated to small piston twins

Aux. How much experience do you have flying light piston twins ?
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