TP13723 wrote:Flight Test Exercises - Ex. 16 - Takeoff [...] B.1 Short-Field Takeoff [...] Performance Criteria [...] c) specify a GO/NO GO decision point to the examiner
Hi all,
I tried searching for similar posts but mostly found discussions on V1 and accident discussions.
When training a PPL student (on say a C172), how would you have the student select a GO/NO GO decision point for the short-field takeoff?
I ask this question because I hear alot of "if we're not airborne by half-way down the runway" on a runway that's 5,000' long. I do not believe this is acceptable although I must confess I have used it before myself. Anyone use the 70/50 rule?
I'll take a short field for example. Let's say it was 700ft to be airborne. I looked at the airport diagram before hand and looked at the runway as I was approaching it during taxi. The second VASIS was about 700ft from the beginning of the runway.
In the briefing I said: I will be airborne at the second VASIS. Did those calculations for a reason might as well apply them.
You can also use other known features such as taxiways, being abeam hangar buildings, runway lights etc,.
Agreed that using a reference like "halfway down the runway" is not a good one for two reasons:
1 - If you're on a 5000' runway taking off with a C150, under most conditions if you're only airborne at the halfway point, there is probably something wrong; and
2 - It makes it very hard to judge where that halfway point is located as you're rolling down the runway.
I would pick something that is easily identifiable like gustind mentioned, taxiways, abeam a hangar, next to a sign... something that you can actually identify when you get to that point down the runway. It should be something that is a good indication of how much space the aircraft needs until rotate, and preferably give you enough space to reject the take off as well. So if you need 1000' to get to the point of rotation, and you have a 3000' runway, pick a landmark about a 1000 feet down the runway.
The take off briefings we used to do for light GA aircraft when I was teaching was something like this:
"If something doesn't look right, feel right, sound right, or if we're not airborne by xxxxx landmark down the runway, then I will abort. Anything wrong after we rotate except for an engine failure will be taken care of above 500' AGL. If we have an engine failure immediately after rotation, I will aim for xxx location. [transfer control to you // if this is a student flying with an instructor or someone much more experienced]"
These are all some good points. If it's a simulated short-field on a very long runway, and there isn't much around as far as signs etc. along your simulated runway length, I like to use runway centreline marks or runway edge lights. For example, if you're in a 172, and you know the distance between two centreline marks is 200', and you have any issues before you get to the 4th or 5th centreline ahead of you, then you will abort.
If you do not have 70%, of your lift off speed by 50% down the runway, then reject.
This assumes, the runway is level, the surface is uniform.
And does not account for obstacles. ( and does not work for skis or floats )
So on short field, pace off the runway,... find or make a marker at half way down the runway.
Then, if you lift off at 50 mph,... you need 35 mph at the marker or reject.
This is a good way to know if you can get out of that 1200ft grass / gravel runway,
on any given day, as most small singles have very little published runway data.
SuperchargedRS wrote:I thought you were talking about short field work. for that I use the 50% rule
Do you really need a no go point for a 172 "heavy" on a 10k runway????
According to the training standards, yes. And if someone happens to be learning to fly at a place where they use a 10K runway, why not start getting into the habit and practicing? It's good to get the students thinking of these things, and also puts into their minds considerations on what to do *after* their go/no-go point should something happen, whether it be an engine failure or an alternator warning light.
Personally, I am very routine based, so I tend to go through the whole thought process of thinking of my way outs and back up plans whether I'm on a 1000 grass strip, or a 10K paved runway. That way it's second nature.
KK7 wrote: According to the training standards, yes. And if someone happens to be learning to fly at a place where they use a 10K runway, why not start getting into the habit and practicing? It's good to get the students thinking of these things, and also puts into their minds considerations on what to do *after* their go/no-go point should something happen, whether it be an engine failure or an alternator warning light.
Personally, I am very routine based, so I tend to go through the whole thought process of thinking of my way outs and back up plans whether I'm on a 1000 grass strip, or a 10K paved runway. That way it's second nature.
OK, I agree in part.
When I am teaching a private student, I let them to get a feel for the airplane, how quick the plane takes to go to full power, how hard it accelerates, the sound of the engine, how engine instruments "in the green" is sloppy/not good enough, if the plane doesn't feel right, or the oil pressure isnt where is normally is (even if it is still a go on a go/no go) they power down and bring it in to the shop. I don't teach a go/no go for huge strips, the exception being if I am trying to prep them for short field d/a work, then I will tell them something like the second taxi way is the end of the runway. They will pick a object, light, whatever that is half way to the end and apply the 50% rule, sometimes I might make it the first taxi way, so they will have to abort.
On most training flight I find it works well to also pull the power for a simulated engine failure at some point, if the student expects you to simulate an engine failure on most flights they seem to always work on being ready for it.
Procedures are good, but shouldn't be used as a crutch for feel & pilotage.
One of my pet peeves is the tendency for FTU's to pretty much ignore the POH performance data. IMO the most accurate method to determine a Go/No go point is to take the POH takeoff ground roll distance and add it to the landing ground roll distance. If the total runway distance is less than the combined total then you don't have a true go/no go point. Just because you have achieved say 70 % of your takeoff speed, doesn't necessarily mean you will ever achieve lift off speed, as anyone who has every tried to takeoff in deep snow or a really muddy field can tell you. Therefor any decision point that is before the aircraft is actually lifting off is not IMO a true Go/No go point.
The good news is for your average piston single the takeoff roll will be approximately twice the landing roll. So you want to be lifting off no later than 2/3 rds of the way down the runway. If you are more than 2/3 rds of the way down the runway then you will not be able to stop without running off the end.
As was pointed out a go/no go point has have be a physical feature that can be referenced to be of any use.
On a related note the flight training industry seems to talk about "short field" a lot but never seems to provide an actual definition of what constitutes a short field. I tell PPL students to treat any field that is shorter than 200 % of the POH landing/takeoff distance as a short field. I have no science to back this up other than a personal opinion. In practice for most simple fixed gear singles, this works out to a runway about 3000 feet long as the cut off. That is short field technique should be used on runways shorter than 3000 feet.
Big Pistons Forever wrote:As was pointed out a go/no go point has have be a physical feature that can be referenced to be of any use.
gustind wrote:You can also use other known features such as taxiways, being abeam hangar buildings, runway lights etc,.
Agreed.
Big Pistons Forever wrote:Just because you have achieved say 70 % of your takeoff speed, doesn't necessarily mean you will ever achieve lift off speed, as anyone who has every tried to takeoff in deep snow or a really muddy field can tell you.
Agreed, however on this particular topic I was looking at the short-field takeoff and constant acceleration (assumed). Unfortunately, our TC over-lords neglect that paved strips are generally longer and if someone paves a chunk of real estate they probably chop the tree down at the end. Meaning that GO/NO GO "dilemnas" often arise on short soft-fields with an obstacle at the end. I guess they don't want to confuse the student and do short, soft field T/Os and landings.
Big Pistons Forever wrote:If the total runway distance is less than the combined total then you don't have a true go/no go point.
So do you not go on the basis of "good" PDM or just go and hope it works?
I remember being taught that there are short fields and there are soft fields. There are no short, soft fields for a given aircraft's capabilities that you should be using.
If you can not accelerate to rotation speed very fast because of a field's softness, it had better be considerably longer than your takeoff run + landing distance and/or be obstacle free.
I agree with using your stopping distance plus a margin for an abort point, but also consider distance to clear an obstacle. This might be longer than your NO GO point allows, letting you get airborne but not clear the obstacles. This is particularly true at high DAs and can vary greatly with pilot technique. Having the nose too high because of approaching obstacles or because you are used to having it higher for low DA vs high DA can really drag it out....
I see the value in the 50% runway 70% of Vr , as a method of getting the Aircraft off a field,
were the POH numbers don't really , or cannot really apply. Such as a 800 asl field and the temp is 26c
the wind is light . The field is grass. Will the aircraft get out at 300lbs below gross weight.
The light Aircraft I fly ( C 170B ) has no takeoff performance to address these variables.
So If I can get 70% of my Vr speeed at or before the mid point , I can safety continue and depart.
to digress a bit at first. Years ago, as a CP, I used to have to train the new hires for off strip and short field work. Here is how it would go..We would take a little flight at about 2000 AGL ( the altitude was on purpose so as not to give them familiarity from circuit altitude) and we would fly over a local strip and I would ask the question. " What do you estimate as the length and width of that strip and do you need to use normal or short field techniques?"
In almost every case I got the deer in the headlight stare? Seems that all these new CPL's had never had one minute of instruction of flying over an airstrip and estimating its length to determine if there was sufficient landing and take off distance.
So lets leave the flight school stuff for a minute and discuss things. As someone mentioned, a good rule of thumb is t/o distance in about 2x landing distance (subject to the same temperatures, moisture, wind , etc. So before you begin teaching the short field techniques, what you should be doing is when you join the circuit look at what a 1000 feet looks like from a 1000 feet., and , if possible start looking at fields if you are in the prairies as 1/4 section is about 1300 feet. Why.. Because before you will take off from a short strip, the chances are you will have to land on it first, so determing the landing distance originally is every bit as important.
You should always..always, when really doing short stip work, consider temperature (density altitude), changed runway conditions, cranky bears. etc. before you ever start the t/o role, and that is hard to simulate with 10000 feet of pavement in front of your 172.
Now. as Wind, Density altiude, water on the surface, all play a part in the T/O, all this nonsense about 50% of runway length is really , well....lets just say it is not necessary.
Same with pacing of the runway. You got into it, so it is a bit late to start determining the distance that way. Here is the technique we use. If there are no obstacles determine from the book, but better from experience, what distance you need. And you should know this..What point do you get A/S indicating. Now try and find some visual reference to choose where if the plane is not performig as expected you will abort. This stuff is not about balanced field length as you might actually need the whole runway to become airborne.
The go/no point then is where you can actually stop before the end. Once past that point you are going aviating or crash. Once by that point, USE ALL THE RUNWAY. If you have runway left dont be pulling it off with the stall horn blaring..( best angle of climb usually, but more in high density altitude situations).and if you still have a bit left over after lifting off and there are no obstacles, lower the nose and use the ground effect to accelerate.
I am aware of the digression, but hopefully some instructors will understand there is more to the short field technique then determining a go/no point.
Now to address your question directly. The go no go point is all about stopping for some. Which if you give it some thought means as you go faster the point moves backward. What you have to do it decide on a performance objective. I am a 100% believer in having a predermined reference point. If you are really doing short field and not play acting, the refernece point makes things a whole lot simpler. Maybe a tree, big rock etc where you say if I am not at 40kt IAS , or my tail wants to lift.or I am not accelrating as should be, I will abort. Then dont forget to do it.
The POH numbers are fine, but in real short field work you also need to know the performance of your particular machine as it pertains to the POH. Big difference between a fresh from the factory engine on a cream puff airframe, and some poor old 15000hr workhorse with its engine 10 hours from its third rebuild.
Lastly, in my longwinded post, C of G and weight are critical in short field work.
Just the thoughts of an old guy who has made his fair share of this type of take offs and landings....and has so far , been really really lucky. More time should be spent in the classroom discussing the variables and techniques then is ever done, from what I can see. It is all about make believe play time. And it is why pilots get into strips in the cool evenings and then crash the next day when the temperature is 30C and they are trying to haul out that old moose carcass
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trey kule wrote:to digress a bit at first. Years ago, as a CP, I used to have to train the new hires for off strip and short field work. Here is how it would go..We would take a little flight at about 2000 AGL ( the altitude was on purpose so as not to give them familiarity from circuit altitude) and we would fly over a local strip and I would ask the question. " What do you estimate as the length and width of that strip and do you need to use normal or short field techniques?"
In almost every case I got the deer in the headlight stare? Seems that all these new CPL's had never had one minute of instruction of flying over an airstrip and estimating its length to determine if there was sufficient landing and take off distance.
If I was a new CPL, I would have given you the same blank deer in the headlight stare. Now that I am a high time low time CPL, I would have told you 'I don't know, why don't we go down and take a look?'
Precautionary landings occupy an entire exercise in PPL flight training and none of them involve assessing a field from 2000 AGL. Pilots who think they are good enough to commit to landing on a strip they have no information about other than a 2000 AGL pass aren't ones I want to fly with. Unless you have an emergency, there is no excuse for not doing a proper precautionary....
There are very few 1/4 sections or range and township roads here in BC...
A digression, but I have to comment. The problem is that the way FTU`s teach, means the precautionary is almost always tacked on to the diversion exercise. Thus it is always associated with an emergency. The fundamental problem is instead of calling it a "precautionary landing" we should be calling it a "landing with precautions". The training emphasis should be that if there is any doubt about the landing area during normal operations, use the procedure. This also doesn't men you have to use the whole meal deal, just that part of the procedure that is appropriate to the situation.
I was actually going to add the 'cookie cutter' FTU precautionary for a 'sick passenger' (unless you are a doctor or can do something about it, fly them to the nearest damn airport! ) isn't always the best. I 'land with precautions' at my field all the time because you never know when a deer or drunk native is going to be on the runway. Going into a completely unfamiliar strip might convince me to do many more passes than the simple 'high, low, land' format of the FTU precautionary.
I never got the impression that the precautionary was an emergency exercise from my training. My first introduction to it was on Trip 8 of my PPL, and the only exercises we did other than that was the circuit, takeoff, and landing. By the time I had done my CPL, I had been off strip and in and out of many airports where I decided to do a precautionary.
I pretty much exclusively flying tailwheel aircraft these days. One of their minor quirks is that when running in 3-point attitude the AS can be inaccurate. Generally the larger tires you put on the mains the worse this gets (or if you've got tall gear to start with). Moreover looking at the AS indicator is a great way to run into something if your dealing with an actual short or soft field because they usually aren't that wide.
In that case what you need is another system. If I place the tail low and the aircraft doesn't get light on the mains by my reject point then we aren't going flying. That isn't to say it has to be airborne but if you've been flying an aircraft for a little while you can sense when it comes alive. Works very similar in any of the training aircraft I've flown, if you rotate before the reject point and the aircraft doesn't get light its time to reconsider. I consider the rejection point to be the POH landing distance from the end of the runway because I know its going to stop in that time.
For me personally a short field is any that I can't do a stop-and-go with 200ft of extra margin at current weight. Solo that would be 1200ft and at gross 1600ft for my aircraft on tarmac at sea level.
There are very few 1/4 sections or range and township roads here in BC...
The magic of GPS where there are no known distance fields. You can actually fly the length of a strip and get the distance, then commit the visual to memory. I was actually only referring to length, and I agree, the correct answer is to go down and have a look, but that was not really the point of the example.
Now to this:
hello from the prairies... where the quarter sections are ~2600' long
I stand corrected. My only excuse for this lapse in memory is old age and my extreme modesty in saying a foot was only six inches .
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) isn't always the best. I 'land with precautions' at my field all the time because you never know when a deer or drunk native is going to be on the runway. Going into a completely unfamiliar strip might convince me to do many more passes than the simple 'high, low, land' format of the FTU precautionary.
