Nice description. Also it’s worth adding that the thrust is following a ‘square law’ with the rpm. So small rpm variations have a big thrust change.

SAS,

That paper contains useful information on tail rotor drive failure and “stuck pedals” but it does not cover the very unusual situation suffered by the Leicester crew.

(I can’t imagine a situation where any helicopter in normal operational flight would need full negative tail rotor pitch).

During a normal Class A rearwards climb, such as this was, the pilot would have been applying a large amount of positive tail rotor pitch.

The aircraft mechanical controls failure suddenly gave him the maximum possible opposite tail rotor input. As I said before, I doubt very much that any pilot would have been able to recover from that situation. I’ve seen it in a simulator many times, both as a handling pilot and watching (and trying to assist and train from the instructor point of view).

This was far more severe than stuck pedals or even total loss of tail rotor power through drive shaft failure and even more so because the aircraft was in a low IAS climb, in accordance with that type of departure. The only hope would be to rapidly achieve full auto rotation and even if that was achievable (it probably wasn’t because of the rapid onset of a high yaw rate) the pilot would still be trying to deal with uncontrollable yaw at very low level - and in the dark!

For those pilots not familiar with helicopters, the closest analogy I can think of in fixed wing terms is for an aeroplane with a high torque propellor engine to be in a minimum IAS climb. The pilot is keeping the aircraft straight using ant-torque rudder. A mechanical failure causes sudden full opposite rudder to be applied, causing a high rotational spin to develop with full pro spin rudder jammed on.

Shy....also remember Simulators "simulate" not "replicate" actual aircraft flight characteristics.

Computers can do only so much despite being very useful bits of kit

We havre to remind folks not to hang their hats on a direct transfer from the real to the surreal in those pretty shiny boxes that oft times reek of someone's spilled lunch.

Plenty of very experienced Aviators have gotten Sim Sick who have never been Air Sick in their careers.

My. post was to offer an analogy that a fixed wing only pilot might be able to use to better understand the basic concepts.

Thanks for that. Explained that way it makes a lot more sense than it did this morning. :ok:

Yes, hence the first line of my post #1216.

There is no way that a manufacturer could obtain fully representative aerodynamic data for all stages of a helicopter going out of control and it’s subsequent flight path…...they would soon run out of test pilots and aircraft. I was lucky enough to be able to work alongside the chap who programmed the sim we worked on and he was always keen to remind us of that fact. In turn, we used to emphasise this to all the RAF pilots we trained. We used the simulator as a sophisticated procedures trainer, not an actual aircraft.

I’ve mentioned before that one of our crews subsequently suffered a tail rotor control failure over the sea and successfully ditched the aircraft in the water with no injuries. The pilot stated afterwards that his simulator training prevented him from doing what he said would previously have been his prior instinct of merely chopping the throttles and entering autorotation. Doing that would have made matters worse in his case, because the tail control mechanism had failed with some positive pitch. Instead he made a gentle yawing descent onto the surface. Despite not having floats the aircraft was subsequently recovered almost intact.

But unfortunately the Leicester accident was a far less benign failure.

I'm one of them SAS, first time in a sim (level D) was for a four hour session, I was first up and got through my two hours keeping stomach where it should, swapping seats I just couldn't take it anymore and bailed, leaving my partner to ride alone. Got better over the years but never at home. Sim instructor explained that very subtle clues can induce the reaction, one was light sources in the visuals not being realistic in that they don't get brighter as you get closer, such as runway edge lighting when flying an approach.

Megan, I noticed that pilots with a lot of hours on the actual aircraft often tended to suffer the most. I put this down to a discrepancy between the “seat of the pants” learning already in memory and what the eyes were seeing. This is obviously a limitation of the motion of a simulator bolted to the floor, partly because the motion gently resets between inputs.

Could be something in that Shy, we typically had a couple of thousand in type (76) prior to starting the sim work.

Certainly remember feeling a bit ropey at times in the Puma sim in Stavanger…..

PCD, Quite a few did. Including one of my colleagues there who later went on to manage the project! :cool:

In my time teaching in the Sim....from the early 76 Simulator at American Airlines Training....to the very much improved Sims for the 212/412 at the FSI facility at the Bell factory.....I only experienced Sim sickness one time....and have never had any problem with motion sickness ever even in very rough water on boats and ships.

The lag between the visual and the Sim is one factor but the most important cause is the way the Sim System works to generate felt forces due to pitch and roll.

In the real aircraft the airframe moves relative to the horizon and once in a stabilized turn or change in pitch attitude that results in a constant relative angle....no other "motion" is felt.

In the Sim....once the "Box" moves per the flight control input....say for example a thirty degree bank.....the "Box" leans over.....and then despite the instruments showing that angle of bank....the Box begins to re-center so it can have a full range of motion available.

Our well tuned hind quarters feel the forces of gravity....and our eyes are seeing something else and the confusion caused by those inputs is what gets us.

The usual victim is the guy not doing much because if you are flying or running the Sim at the Control Panel....each are "busy" and are not free to focus upon the odd sensations.

I was asked if the Pilot had shut down or reduced engine power by means of the ECL's or throttles....and could not respond to that question.

Does anyone know of a reference to that in any official report or discussion?

FYI - The AAIB have announced that the report is scheduled for publication 6 September 2023

https://www.gov.uk/government/public...investigations

Document lists another AW helicopter tail rotor duplex bearing failure. Found during post-flight inspection. Phew!

13 Jun 2022 G-CIMU AW139 Failure of tail rotor duplex bearing found during post-flight inspection, Norwich Airport

Leicester — Scheduled for publication 6 September 2023

If they keep to that schedule that will be four years and ten months after the accident. Guess the billionaire family didn't like the report?

Maybe the manufacturer has been the issue preventing it’s publication.

AAIB Report here.

https://www.gov.uk/aaib-reports/airc...o-aw169-g-vskp

Introduction:

The Air Accidents Investigation Branch (AAIB) became aware of this accident during the evening of 27 October 2018. In exercise of his powers, the Chief Inspector of Air Accidents ordered an investigation to be carried out in accordance with the provisions of Regulation (EU) 996/2010 and the UK Civil Aviation (Investigation of Air Accidents and Incidents) Regulations 2018.

The sole objective of the investigation of an accident or incident under these regulations is the prevention of future accidents and incidents. It shall not be the purpose of such an investigation to apportion blame or liability.

In accordance with established international arrangements, the Agenzia Nazionale per la Sicurezza del Volo (ANSV) of Italy, representing the State of Design and Manufacture of the helicopter, appointed an Accredited Representative (Accrep) to participate in the investigation. The Transportation Safety Board (TSB) of Canada, representing the State of Design and Manufacture for the helicopter’s engines, the National Transportation Safety Board (NTSB) of the USA, representing the State of Design and Manufacture of the tail rotor actuator and the Bureau d’Enquêtes et d’Analyses pour la sécurité de l’aviation civile (BEA) of France representing the State of Design and Manufacture of the tail rotor duplex bearing, also appointed Accreps.

Experts were appointed by the Aircraft Accident Investigation Committee of Thailand and the State Commission on Aircraft Accidents Investigation of Poland.

The helicopter, bearing, tail rotor actuator and grease manufacturers, the operator, the European Union Aviation Safety Agency (EASA), and the UK Civil Aviation Authority (CAA) also assisted the AAIB investigation.

BBC already making a headline of it.

https://www.bbc.com/news/uk-england-...shire-66716572

also an interesting video reconstruction available on the BBC link - they never stood a chance...................

Bearing seized, drive shaft unscrewed = total loss of any yaw control at all

A sobering read, but a small comfort for those involved that it was one of those rare events - a true accident where the people there really couldn't have prevented it. It's assuring to see that Leonardo and EASA have published a raft of SBs, ADs and revisions to the airworthiness standards, as they should.

G

One of those rare "old fashioned" accidents that we used to have quite regularly but learned from them to initiate better design & oversight criteria. In some ways it shows how far we have come over the last 50 years. Unfortunately helicopters, more than fixed wing, generally have catastrophic outcomes when it comes to failure of Critical parts. No solace to those lost that had no virtually no chance, but hopefully the industry will not see a category repeat.

If the tail rotor control push/pull rod running through the outer drive shaft had been designed to "free float" in rotation, rather than held stationary by a single nut, this failure wouldn't have happened. Hopefully this will be taken into account in future designs.