What's a "maximum performance takeoff abort - backwards." ?
 

Is this something you do with float helicopters (Mariners) ?


NTSB Identification: SEA04CA122.

14 CFR Part 91: General Aviation
Accident occurred Monday, July 05, 2004 in Hillsboro, OR
Probable Cause Approval Date: 9/29/2004
Aircraft: Robinson R22 Mariner, registration: N856HA
Injuries: 1 Minor, 1 Uninjured.

The flight instructor reported that they were in the process of practicing

"maximum performance takeoff abort - backwards."

The student was on the controls during the maximum performance takeoff phase to an altitude of about 150 feet above ground level, and the instructor took over the controls to demonstrate the abort procedures. The instructor took the controls just prior to call for the abort. When the abort phase began, the instructor applied aft cyclic and slightly lowered the collective. The helicopter had been in a tail low attitude and started to descend into "settling with power." The instructor applied forward cyclic and lowered the collective, however the helicopter did not have sufficient altitude to level out or gain airspeed to recover before impacting the ground on the right side skid. The helicopter pivoted around about 180 degrees then rolled over onto its left side.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot's failure to maintain aircraft control resulting in an uncontrolled descent and subsequent roll over. Low altitude flight and the pilot's encounter with settling with power were contributing factors.

I haven'theard it called that, but it sounds like trying an abort from a CAT A / CAT 1 take off. This can be where you depart up and back,so if you abort prior pre determined decision height, you have the deck in front of you. This profile is as far as I know for twins only, and supposedly ensures landing spot until at a height to clear the rig and enter auto if needed. I really don't know all the details, so maybe someone with lots of rig experience can fill in a bit more.

My reading of the same report gives me a different interpetation of what happened....

"When the abort phase began, the instructor applied aft cyclic and slightly lowered the collective. The helicopter had been in a tail low attitude and started to descend into "settling with power."

It sounds to me like the aircraft was moving up and maybe forwards and as in an attempted takeoff at marginal power does not work....he was trying to land back at the takeoff point. If they were facing into wind...he could therefore have backed into his own downwash and the rest as they say is history.

I did not take it to be a rearwards takeoff but rather a rearwards reject. All the more reason to utilize the non-American method of rising vertically until clear of the barriers by a safe margin then starting your transistion into forward flight. The American method that evolves from the US Army method as adopted by the FAA uses a forward movement all through the takeoff to clear the barriers by a safe margin....which means one gives away clear way prior to clearing the barriers.

Long ago I adopted the Non-American method....in that I take the best from the many different ways to answer the same question.

SASless,
"non american method".... That's interesting, never heard of that.
Is there a non american method for landing in a confined area as well?

I am currently clearing land in my back yard for an approach, so this is of interest to me.
Thanks,
slowrotor

Once again, words get in the way of good communication.
What exactly is a 'maximum performance takeoff'? I've never seen it defined any place, so if any ppruners can show me an official definition I'c be grateful.
Does it mean 'using maximum power available', or does it mean 'simulating no more power is avalable and this is all the performance I'm going to get'.
Does it relate to a vertical takeoff? or having to do a level acceleration from a minimum skid height? Or what does it really relate to?
(I'm thinking that there will be at least three official definitions....)

Shawn,

My take on this is much as I said earlier. My training was in the US Army, and much of what I see in the FAA handbooks is exactly the same as I recall the Army techniques to be.

We had normal takeoffs, max-performance takeoffs, and confined area takeoffs. Our British friends have normal takeoffs, towering takeoffs, and confined area takeoffs. Similar concepts....different names and except for the confined area takeoff...pretty much the same techniques.

I remember max-performance takeoffs as being vertical ascents to 100 feet agl then a transition into forward flight. Towering takeoffs at Redhill were the same maneuver.

It would be an interesting exercise to compare the CAA/FAA/MOT handbooks for helicopter flying....to see how the various topics compare.

My understanding of it is/was that you climb from 'skids light' on the ground and pull the maximum manifold pressure available (based on OAT and field elevation), then when you reach the require height to clear the obstacle your transitioned into normal forward flight attitude.

PW

Pilotwolf -I recommend using maximum power required rather than maximum power available.

Not a CFI but believe to demonstrate and teach the procedure a maximum mp is agreed rather than use all the power available. I know a CFI who will put his hand on the collective to stop it going any higher to demonstrate what happens when you try to pull power you do't have.

PW

This may help in the description and problems associated with a max performance takeoff.




http://www.copters.com/pilot/max_takeoff.html

I confess that just from reading the accident report, I have no idea whatsoever what the instructor was doing or why. He says the aircraft was in a tail-low attitude when he initiated the abort, which may indicate that the takeoff was being done to the rear, but I can't tell from the narrative if this was the case.

Perhaps another case of a low-time instructor teaching something he didn't really understand. Can't tell that either, though, without more information.

Thigs that make you go hmmm..

I kinda have an idea of what he was trying to do. One thing I see alot of guys do is on there Max Per T/O is pull in all the power rise stright up or real fast on the departure path to clear all the obstacle's. In the real world flying light singles in feild this doesnt always work and has a few disadvantges:
Remember most fo the time you are at MGW limits:) big drillers, juggies, fire guys etc and are heavy on fuel.

I look for the least steep approach out of there (not always directly into wind).

Pull in max required power and very SLOWLY depart on my departure path (usually moving forward slightly if possible). The reason I go real slow and controlled and try and keep that constant angle is if I am not going to be able to make it I can back down to the the same path to my spot. Lot of thing can happen, I could be too heavy for conditons, the wind could be 100% different at the tree line, I may get a light that requires me to land asap.

Well I dnt know a whole lot bu thats what i do , and I can see what the instructor may have been tryingto do.... Just wait unitl he sees how confined these confined areas can relly be!

RB

What is a "Maximum Performance Takeoff"?

Boiled down, you have a set of priorities:
1) Don't get anybody killed
2) Don't crash
3) Don't damage the aircraft
4) Don't violate any rules/FARs
5) Get out of the area as planned

"Maximum performance" has two facets:
First, it means extracting maximum required performance from the powerplant and rotor system, in order to minimize the time spent in an unfavorable portion of the H/V curve, and to ensure that you are clearing hazardous terrain ASAP. Some will say to always keep a little power in reserve "just in case", but if you end up needing to tap that reserve, it would have been better if you had been using it all along, as you would have been that much higher. If required, use all the power you have until you don't need it anymore. (I restate the obvious when I say that optimum RRPM is part of maximum airframe performance)

Second, it means utilizing the flight path that will ensure the maximum aerodynamic performance. For example, if you have the room to get to ETL while still having an abort option, take advantage. If you know that the wind will be stronger once you get above the treetops, you might choose to ascend vertically until you get the added wind, then move forward, ect.

Again, there are too many variables to lay out THE WAY of doing a "max performance" takeoff, but there are a few guidelines:

-unless you are getting shot at, you must ensure that you can safely abort the takeoff up until you know that you will definitely make it out of the area. If you almost get out, you want to be able to return safely to the ground.

-in the balance between possible hazard from engine failure vs tangible hazard from challenging the obsticle, choose the best odds, but minimize the time spent hanging off of the engine. I'd rather spend 15 seconds hovering at 100' than five seconds watching trees looming ever larger while wondering if we're going to make it.

-your goal is to minimize the time spent with poor options, and to balance those options in favor of survival if the worst happens, keeping the original priority list in mind.

You want to get the aircraft out of the area with the maximum level of safety possible. You are always balancing the small (but omnipresent) chance of an engine failure against the larger chance that pilot error - miscalculating performance, misjudging wind and distance - will force an aborted takeoff, or possibly lead to settling if you are "hovering back down" after almost getting over those 150-foot trees. You are better off to trust the engine rather than your ability to infallibly judge how the aircraft will perform.

Hope this helps

I'm surprised all you experienced guys haven't really heard of this. . .

Max Performance take off is distinguished from a Towering take off by the fact you need a few feet between you and the obstruction.

As you lift you inch it forward immediately in the hope you will gain ELT (12kts - ish) and pull in more lever as soon as the power is available.

Never heard of an abort procedure for this but I assume the chap above (as previously stated) was trying to get back to where he started from. . Not good.

If you don't have the room or the power a vertical take off spinning to the right (non-French) will save you valuable power. . . Don't know what this is called but . . it really works.



:ok:

Mr Selfish
 

You serious? ELT on main rotor.

Don't know - I asked my instructor the same thing after the demonstration, I guess thats where pure skill comes in. . ?

In this case, I don't think I would have lowered the lever. I think it might be better to keep the ROD below 200fpm If not possible try for fwd speed in another direction . . and perhaps spiral back down?

But hey, what do I know. . :hmm:

!!!!!, I meant ETL - Effective Translational Lift (just got back from France, sorry)

For a definition of maximum-performance take-off, see the Rotorcraft Flying Handbook, the official FAA text on helicopter (and gyroplane) flight training. The maneuver is as Sasless describes it, and does include forward movement as soon as the climb is started. This is what examiners are supposed to look for, and what CFIs are supposed to teach.

The question of what to do if you can't make it out is never considered, apparently. A vertical climb, allowing a vertical descent, or even fall (in case of engine failure) to a spot you know you can land on (you just did) is a far superior move IMHO.

I have been teaching both JAA & FAA sylabus recently, and for what its worth this is the short hand of what I taught at the school I worked at.

FAA. maxP take off:

From low hover OR surface to lift off and maintain attitude for either VX or VY depending on what you need, but usually VY. Power (TQ /MAP) often being limited to simulate higher DA. Once clear, accelerate to normal climbout. Height over speed, then speed over height to increase safety margin if it all gtes quiet.

JAA:

First option is to try the VERTICAL take off, with a controlled steady climb (no stick stiring either). If unsuccessful, note max power available AND make judgement of obstacle clearance shortfall and available distance.

Descend in controlled maner, using the front and side transits to keep your landing spot below you. The towering take off is then used (if you judge it will work) and using the same vertical transits, break hover verticaly and at a higher rate of climb, before loosing ascent rate, transition very carefully into forward flight.

So basically the towering is the same as an FAA maxP, but it starts forward transition at almost obstacle height .

Brian:
What is VX in any particular helicopter? The number is never published, and not required to be in any flight manual I've ever seen.
If you have enough power to climb vertically from OGE, then VX is going to be zero. If you don't, VX is probably somewhere below where the pitot system works sensibly.
VX is not a term that I've ever seen in a helicopter flight manual.

Terminology again! Love it.

In Oz we would call this manoeuvre a limited power take off. When I went to the states on UH60L and was asked by my instructor to demonstrate a "max performance take off" there was just the two of us on board, and half fuel. I promptly asked "are you sure you want to do this?" not for a minute realising that what he wanted to see was a limted power take off. When he replied "yep, sure do son" I got clearance for take off at the sattlelite airfield we shared with 9 other Black Hawks, lowered the nose sharply and pulled to 100% matched TQ and jeepers, didn't we take off? Instructor goes white going through 60 kias at over 4000fpm up and the guy in the tower yells "yeehar Aussie go get em"!! We decided to check terminology after that!

The accident report is, I hope, not the full report. I make the following off the hip observations about the report, but accept that I wasn't there and therefore do not really know the story:

Firstly, the report predictably blames settling with power. As do 95% of US accident reports where they really are not sure what happened. As most of you will be aware, we have had a concerted campaign on other threads to rid the world of this misleading terminology, and replace it with Vortex Ring State (VRS), because that is what it is. This will avoid confusion with the term "power settling" which is also problematic and better called "insufficient power".

Secondly, there is no way that this accident was VRS. Do a search on this topic in pprune and read the posts by Nick Lappos (lets not get into that arguement again here).

Thirdly, from the report it appears that the instructor was teaching aborts, but for some reason took over when the tail was already low, and then allowed the aircraft to go backwards whilst lowering the lever. My first observation about this is that it seems strange that an instructor would break an instructional sequence down like this as it easily leads to confusion. Why wouldnt the intsructor demonstrate the whole sequence first, then get the student to fly the whole sequence so as to avoid these kinds of confusion creating situations?

Fourthly, Once he had placed the aircraft into a backward, tail low low power and OGE situation, it will require alot of power to recover. This suggests that the mistake became an accident due to lack of available power to recover from the situation he placed the aircraft in, particularly given that he would have to pass through some turbulant air from his downwash in the recovery. As he passed through some turbulance, and applied max power but was still descending, it is tempting to assume you are in VRS, but almost impossible. This is simply an "insufficient power" situation where there was insufficient power to arrest the rate of descent set up.

I must add that VRS is a very understandable assumption, and I would question whether or not I would have picked up the differences in time to avoid the accident, but I doubt it.

What we can learn from this one is ensuring that when teaching limited power operations you ALWAYS have an out. There is no point practicing bleeding. Use an obstacle like a single tree in a field and get as close to it (or as far away) as you like to set take off area distance, and aim to attempt to fly over it pretending that it represents a solid wall in front of you. Use an artificial power limit BELOW the power available so you DO have a power margin for recovery. If it all turns to worms, you simply head either side of the tree into the clear field and use your extra power available to recover.

But all this is in hindsight. And hindisght is the view of an ar5ehole.
:ok:

Shawn,

I tend to agree with you that Vx is a less than useful concept in helicopters due to the ability to climb at zero speed; it is also correct that due to the inability of the ASI to operate at low speeds it is difficult to set or note the passing of other esoteric points such as Vstay-up on a twin (we might wish to use this for analysis of low speed operating regimes on systems such as HOMP (flight data monitoring)). (The UK CAA is at present seeking to establish an accurate method for low airspeed measurement (to be used only for post-flight analysis).)

However, with respect to the subject in hand, Prouty does give some guidance on the techniques for limited power take-off and also describes a method to establish the best angle of climb - at the end of his paper on Critical Take-off.

http://safecopter.arc.nasa.gov/Pages...L_TAKEOFFS.pdf

Shawn:

Fair point about the low air speed accuracy of the ASI.

I should have been less lazy and typed "best angle of climb" as opposed VX, and "best rate of climb" instead of VY.

Best ROC, as you corrected, is zero if the power is sufficient, and I believe that at limited power (insufficient power levels for vertical) it is the point where the tangent touches on the back side of the power required Vs air speed curve, drawn from the "given available power limit of the day. However there is definitely going to be a margin of error involved in establishing that flight performance. What I was trying to get at, is that "best angle of climb" will be at a slower air speed than "best rate of climb".

Question: Do you think that given an accurate power required curve table, that "best angle of climb" speed could be judged reasonably well for different max available power figures.Referenced from disk attitude, set by experience coupled with GPS ground speed on a calm day?

Brian I think for most helicopters that 'best angle of climb with limited power' speed is going to be between 30 and 40 kts, but few helis have an ASI accurate enough to indicate it. If you know the wind speed accurately and have a method of measuring groundspeed (doppler/GPS etc) then you could get close but disc attitude is not a measurable factor. If you feel the aircraft attain ETL and can maintain it then that is your best chance of managing a steep climb out but I am firmly with SASless and the JAA regarding the use of a vertical climb until above obstacles and then transitioning. If you don't have enough power to do this you need to ask yourself if you should have less pax or fuel on board and how desperate are you to get out of the site before trying the FAA/US Army 'lets fly forward and hope we clear the obstacles' technique.
I know the Australian Army favour a technique where they try to accelerate to a suitable climbing speed but they identify and brief an abort point so that the aircraft can be safely brought back to the hover before reaching (impacting) the obstacles.
Back to the original post - this seems like an instructor trying to demonstrate something he doesn't really understand - a rearwards descending abort for God's sake - it doesn't get more dangerous than that (much).

Crab

Please don't think I am championing the "'lets fly forward and hope we clear the obstacles' technique." either. I am also very much in favour of the JAA / Canadian method, over the max Perf tecnique :ok:

The best system I have come across so far for limited power take offs was the UH-1H techniques developed by the Australian Airforce. They divided all departures into 4 categories:

Category 1 can only be attempted on a runway style environment and is used with no requirement for power margin, ie you may not even have enough power to hover IGE.

Category 2 is used in open confined areas, and is what crab refers to. Before departure, you determine the last point of safe hover in the pad, then about half way between you and that point, you determine a decision point (abort or continue). The technique is to draw a line from your hover to the top of the obstacle you intend to clear. Simply apply max power available whilst adjusting cyclic to fly that imaginary line. At the decision point, it is easy: if you are achieving the line and will clear the obstacles, continue. If you have fallen below the line, abort to your last point of safe hover. You need a minimum of IGE power plus 3 psi (6%) to attempt this up to a max of a 6 degree departure angle (this number may be wrong: my memory is fading), and there is a table that determines margin required for steeper angles, up to about 18 degrees.

Category 3 is what the JAA style technique is. A verticle departure is made pulling max power available. The abort point is directly below you, or slightly to your front if the LZ allows, and a transition can only be made by lowering the nose if either the rate of climb is significant, or for heavier aircraft once attaining about 100 ft above obstacles. Obviously, terrain and obstacle shapes are also considered. No power margin is required for attempting this manoeuvre, and it is acceptable to try this if you do not have a Cat 2 margin available.

Category 4 means not limited by power, and is required for all hoist operations, NOE, and OGE required manoeuvres such as an OGE arrival requirement. You must have OGE hover power plus 3 psi (6%) to be "Category 4", ie basically unrestricted by power availability.

The charge at the trees and cyclic pull up style manoeuvre is considered a wartime manoeuvre only, where the high risk of tree/obstacle strike is less than the risk of not going!

When I was at NTPS, we had a very accurate GPS for post-processing takeoff data. We did some exercises in the UH-1N and had the students rotate at different airspeeds (as low as 35 KIAS if I remember correctly) and climb out 10 KIAS faster.
(We tried using GPS, but found that it didn't have a fast enough update rate to be useful in any way. it would read very low values for quite a while and then suddenly be close to what you were at in a steady climb. Not useful at all for anything dynamic.)
What we found was quite astonishing. The airspeed system simply could not keep up with the reality - (bear in mind the UH-1N has the airspeed boom on top of the roof, not out from the nose like the 212/412 so these results may not be appropriate for those models). If we cross plotted airspeed with the real speed (we did all these tests in a no wind day) we found that when the airspeed indicator was saying 35 Kts, you were really doing 50 Kts.
Sadly, the low airspeed indicating system we had was not serviceable, as I dearly wanted to prove that it might have a useful roll in getting better angle of climb performance at a very low and repeatable airspeed.
And the problem with defining one speed for the climb out is made worse by trying to define how much power you have available to make the tangent point from....

This is all great stuff, particularly the difference between simulated and real max power take off, but it seems no-one really knows what this instructor was up to ?

It appears s/he either took off backwards in a Cat A type profile intending to abort forward (showing off and pretending to be flying to the rigs ?) or took off with the intention of aborting backwards to the take off point ?

I've only ever done two Cat A take offs so can't comment but would someone in the know care to explain the abort bit and/or whether it would ever be SOP to abort backwards ?

I ask the latter due to the reference to it being a mariner so maybe this is what you do on/off a boat or deck ?

Aborted take off
 

Never heard the like of a backward aborted take off. How can you see a reject point.
A Group A take off if I remember correctly for the Puma is.
Take off with a slow rearward movement and gentle climb so that you can reject at any time to the take off point
At Decision Point of 100 feet call decision and rotate from this point you will have sufficient height and power single engine to go around should the other one fail.
Really restricts take off weight so does'nt tend to get used very often offshore. Probably only be used to come out of a confined area, hospital helipad, after dropping casualty brought in from a rig.