AAIB November 2005

[Hilico]

Enstrom goes down, fuel exhaustion - engine manuals have consumption figures but a/c manuals don't - here. (http://www.aaib.dft.gov.uk/sites/aaib/publications/bulletins/november_2005/enstrom_f_28a_uk__g_baau.cfm)

Loss of control while taxiing in R44 - LTE. Here. (http://www.aaib.dft.gov.uk/sites/aaib/publications/bulletins/november_2005/robinson_r44__g_sytn.cfm)

Edited to add: Before we get into any arguments, 'LTE' is a quote from the summary.

[muffin]

Shrewsbury does seem a bit off track when returning from Nottingham to Barton. The course deviation on the return flight must have been considerable.

[Gaseous]

Were it not so difficult to get the required approval to fit modern instruments to old aircraft, we would not be misled by rubbish, old instruments. This case indicates that inaccurate instruments are worse than useless.

While it was somewhat naive to assume that the thing was burning under 60 lbs/hr full rich, it is quite likely that the gauge said that. I am familiar with the instrumentation in a few old Enstroms and it is all rubbish, yet we are forced to retain it.

It is simple and comparatively cheap to buy STC'd, accurate instruments. It is almost impossible to get permission to fit them.

The 'safety regulation' in this case is counter productive and makes flying more dangerous than it needs to be.

[headsethair]

With regard to the R44, RHC will most likely go ballistic at some of the statements in this report. LTE was plainly not the cause of this incident - the cause was a low-hours pilot who had only flown 1 hr in 90 days and had only 7 hrs experience on an R44 (out of just 58 hrs in helicopters.) And was flying with 2 pax! Jesus.

These figures are in the report - as is the curious statement : "Despite full left pedal input, however, the aircraft continued to yaw to the right. During this manoeuvre the nose pitched down and the main rotor struck the ground." This is an aircraft with little forward motion, a small wind from behind........and the main rotor struck the ground before the accident happened ? Given how high an R44 rotor sits (and assuming it was running above 90%), this would have to be an extremely strange thing to happen without someone making it happen.

It's interesting to note that the report spends much more wordage with a CAA/AAIB a**e-covering exercise than it does reporting the investigation.

Good to see "A comparable article for the general aviation community will be published in the first 2004 issue of the General Aviation Safety Leaflet (GASIL)."

That'll be 06 then ?

For the spotters: 2nd AAIB report for G-SYTN. The first one (under original owner) was a tail chop.

[helicopter-redeye]

I recall the first G-SYTN accident was the tachs suddenly reading zero and the pilot heading for the ground thinking the engine had failed.

'Tis cursed. Beware, the person who has bought it for salvage ...

[headsethair]

De-registered 28/10 and sold to Ukraine.

[Mikeb]

G-SYTN was my machine, flew around 150hrs trouble free in her.
Tail chop accident was the previous owner.

I had two incidents with the machine, first one was a R22 pilot doing his rating to R44. Overspead the engine on startup for his check ride, 17K damage.
Second incident was the crash mentioned in the AAIB report. Total write off.

Both incidents were low time pilots who had the minimum time required to fly the 44.

The moral of the story is don't let a new ppl use your 44 solo if they only got 5hrs on type.

Headsethair, your correct the machine has been sold to the Ukraine, I'll be amazed if it ever fly’s again after the damage it sustained.

[RobboRider]

Headsethair

I have to admit I have missed your reasoning.

"LTE was plainly not the cause of this incident - the cause was a low-hours pilot who had only flown 1 hr in 90 days and had only 7 hrs experience on an R44 (out of just 58 hrs in helicopters.) And was flying with 2 pax! Jesus."

Thank God most R44s are too silly to pick when their pilots have only 7 hours on type - otherwise every pilot will have crashed at 7 hours into their logbook. This must have been a very astutue R44. :E

The description of the accident sounded like LTE is a reasonable assumption.- The fact that the pilot had very little experience is what may have allowed LTE to develop.
As a cause of the loss of control this could easily progress to a loss of horizontal stability which could have caused the blade impact - LTE is a reasonable diagnosis of the initial loss of control.

I will agree that Robinsons have an excellent tail rotor design and are not known for LTE but that doesn't stop it happening if the conditions are right. I don't think RHC will need to defend the machine - It's been put down to pilot error in conditions where Robinson's already have an enviable record.

[[email protected]]

Robborider - I agree with headsethair, this was not LTE, I suspect the TR was producing as much thrust as it was designed to at the time of impact and had not lost its effectiveness. The pilot mishandled the aircraft and it did something he wasn't expecting and didn't have the skill to either prevent or correct. Verdict - pilot error.

I think Headsethair's point was that if you haven't flown more than an hour in 90 days then taking pax in an aircraft you are barely familiar with is probably a pretty crap idea.

Skill fade is real and it is a killer.

[headsethair]

LTA I could agree with. But not LTE. I am surprised at the AAIB's choice of language.

[RobboRider]

Headsethair,

I do agree with your comment about lack of recent experience. 1 hour in 90 days is not enough and one hour in 90 days with only 58 hours total is a recipe for getting into trouble.

crab

Yep Skill fade is especially rapid when you've got very few hours/experience to fall back on.

HSHair

I presume by LTA you mean Loss of Tail Rotor Authority and by LTE Loss of Tail Rotor Effectiveness . What is the difference? I thought they were the same thing?

cheers
RR

[headsethair]

RR: a personal view. LTA is overpitching of the tail rotor - so pilot-induced. LTE would be the failure of the TR to produce enough thrust despite being at full pitch with max available power - as in the recent discussions regarding the 206 TR and its apparently inherent apptitude for developing LTE.

You have to work really hard to get LTE in a 44. So hard that LTA is what you'll achieve!

I looked back to other discussions - here's what Nick Lappos said about LTE last year:

"Most helo pilots can't experience LTE becausae most helos cant get LTE.

The term LTE makes me wince. The concept of the tail rotor somehow losing effectiveness is a convenient one for folks to use, because it allows the people who make small tail rotors to blame a mysterious force of nature instead of fixing their problem.

There are two possibilities for an LTE event to be triggered. They are both the result of you having entered a region where the tail thrust is not enough to counter the main torque because the main torque rose by itself.

They are neither because the tail rotor suddenly experienced massive reduced thrust.

LTE is almost always because the tail rotor has too little thrust BY DESIGN to account for small normal reductions in its thrust. Typical thrust variations of 5% are easily handled by tail rotors with that much margin above the thrust needed to do their jobs. When a tail rotor has no margin, by design, these 5% variations are too much, and the main rotor torque dominates, causeing loss of yaw control.

The two cases cited by hilico show how the term has now been so badly abused as to have entered the lexicon for any pedal stop event. An overloaded helo that runs out of yaw control does so as its tail rotor is producing thrust well in excess of its design capability. The tail rotor is not the cause.

LTE is a term invented by the team from one manufacturer who has to quickly train a bunch of pilots to compensate for a marginal yaw control. the worldwide data base shows that about 95% of legitimate LTE events is experienced by one type of helo (the 206).

Look at the hover curves of several helos to note that the hover weight is not determined by the power, it is determined by the tail rotor design thrust. These are prime candidates for "LTE" because the have "Tail Rotors Too Small".

Please, to be precise and to teach proper procedure for recovery, do not call overpitching and loss of yaw control LTE, call it overpitching."

[[email protected]]

Headsethair - I think you might have got the wrong end of the stick with the overpitching scenario - Nick wasn't talking about overpitching the TR but instead the MR. As the Nr decays because the engine can't output any more power to drive the MR, the TR slows down and becomes less effective, reducing its thrust.

As to LTA - I dont think hitting the pedal stop is LTA - that term is usually reserved for situations where the control movement of the TR is reduced or lost due to cable breaks, AFCS malfunctions or hydraulic problems. The tail rotor is still spinning round but you can't effect the normal range of pitch change on it.

Back to pilot error for the R44 pilot.

[Buitenzorg]

There is one phenomenon I’ve never seen addressed in these “LTE / LTA” accident investigations that most of us, certainly those who have spent time giving primary instruction are familiar with. It has no “official” name but my vote would be FOC, for

Freezing on the Controls.

From my own primary flight training efforts I recall (with cheeks burning) those occasions where despite my pushing that left pedal for all my 200 lbs. was worth the nose merrily kept trundling to the right – until the instructor took over, I lifted my trembling right leg off the pedal, and miraculously another 2 or 3 inches of pedal travel materialized.

I experienced an even more extreme example of this while giving instruction a few years later. My student was a slightly-built PPL rated gentleman in his 60s; I was in my 30s and outweighed him by over 50 lbs. Nevertheless, on several occasions after I called “I have the controls” I could not budge any of them – not the pedals, not the collective, not the cyclic – because of how tensed up he was. I terminated the lesson early because I was afraid we’d crash while wrestling for the controls; next morning he flew with another instructor who outweighed me by about 40 lbs. thanks to his weight-lifting hobby, and despite my warnings about this student he thought the pedals had jammed the first time he tried to take over.

These experiences have led me to believe that in a lot of cases where the accident report read “despite application of full left pedal” it should have read “despite the application of what the pilot believed to be full left pedal but was somewhat less than that”. Typical scenario: low-time and/or out-of-practice pilot, already somewhat tense, tail- or cross-wind hover, a little gust and the nose whips right, pilot really tenses up then pushes the left pedal, but against his tensed-up, immovable right leg, pilot now believes he has full pedal in and why doesn’t this spin stop? The remedy here would be enough clarity of mind to consciously lift the right foot off the pedal, but in a high-pressure and rapidly-changing situation, that’s an awful lot to expect from a relative neophyte. If the investigators asked “did you have your right foot on the floor?” and the pilot answered in the affirmative I’d have to believe he really had full left pedal in, but so far I’ve never seen this confirmed either way in accident reports.

As for my personal experience in type: in 250 hours in the R44 including hovering in and out of ground effect in any relative wind angle, I’ve never encountered the pedal stops. The tail rotor authority was always excellent. Please note that “twitchy in yaw” is not the same as “poor tail rotor authority”.

If the subjects of discussion are “Gazelle” and “fenestron stall” replace left with right and vice versa in the above.

[[email protected]]

A good point well made Buitenzorg - I have had to shout at students to make them let go of the controls and on one occasion I was convinced I had a TR malfunction as I couldn't budge the pedals in a 60 degree bank turn (a very strong student just like yours).
It is a common fault when instrument flying in actual conditions, the extra apprehension felt by the student makes them involuntarily tense their legs and their strongest leg pops the balance ball out in the opposite direction.