...whilst we peruse a report into an R44 R1 Clipper accident which occurred in the December of 2020.
I was pointed in the direction of this accident report (plus a video of the accident itself filmed from the ground) as it was thought that some valuable lessons could be learnt from the accident for the benefit of both current and future pilots.
Certainly, the use of accident reports as a flight safety medium is one of the primary reasons for such reports; the prevention of similar accidents.
There is the old adage that “You must learn from the mistakes of others. You can’t possibly live long enough to make them all yourself.”
However, I have cautioned before that when reading accident reports it is very easy to convince yourself that you would not make such a fundamental mistake or error!
If you start to think this, just pause and ask yourself if the pilot had deliberately gone out to have an accident?
Hopefully, you will arrive at the obvious conclusion that no, they did not.
Therefore, it must have made sense at the time or they were overwhelmed by events.
The UK AAIB published their detailed report in 2021
The idea of this particular article is to further discussions between instructors, students and pilots for the reasons I give above and to consider the possibility of other factors that may have been taken into account during the accident investigation but are not considered in the text of the published report.
It is by no means an analysis of the accident itself and it should be clear that I was not involved in the investigation.
The said accident involved an R44 Clipper 1 but it looks as if it was equipped with standard skid gear at the time of the accident.
I mention this as it is an important point in relation to the possible weight of the R44 at the time of the accident.
Unfortunately the aircraft weight is not mentioned in the report but I doubt if the R44 was at gross weight with 3 souls onboard.
The accident site was in the area of Holmfirth, North Yorkshire, which has an elevation of circa 500ft.
It was a cool day at +8°C with a dew point of +5°C (not hot and high).
Good visibility greater than 10 km with a wind speed of 14 kts from 210°.
This recorded information was taken from Leeds/Bradford METAR at 14:50.
The accident is recorded as having taken place at 15:30.
The accident happened during an approach into a confined area.
Unfortunately the pilot misjudged the wind direction and therefore made a downwind approach to his intended landing area.
The result was that the R44 experienced a heavy landing.
The report extensively covers areas of ‘over pitching’ and ‘vortex ring state’ with good explanations of both.
The conclusion reached in the report was that the helicopter hard landing occurred due to a downwind approach and an attempt to flare the aircraft.
The main rotor was over pitched when the engine had reached its rpm limit causing a high rate of descent and an uncontrolled yaw to the right before impact with the ground.
At this point I think I should point out that there is a slight error in the above text from the report as I think it should state ‘power available limit’ and ‘not rpm limit’.
For what it’s worth, below are my two pennies worth on what might be further considered in order to expand the discussion on other possible causation factors in the said accident:
The R44 Clipper 1 has a 260 BHP engine, and yes, it’s de-rated to the following limits:
- 205 BHP maximum continuous power (MCP)
- 225 BHP for 5 min (takeoff) but subject to the pilot operating the controls correctly, there should be nothing to stop a pilot using the 260 BHP available if needed to prevent an accident
There is a caveat to this as the engine has been de-rated by RHC via engine rpm.
At 102% indicated on the dual tachometer, the engine rpm is not at Lycoming’s maximum of 2800 but at 2718 rpm (power being directly proportional to rpm so hence the engine has been de-rated).
Actually, for the engine to develop 260 BHP the pilot would need to open the throttle to take the rpm up to 2800, which would be 105% indicated.
Subject to not knowing the aircraft weight and serviceability state of the engine at the time of the accident, I would think that there should have been sufficient power available to prevent the accident.
So what could have prevented the pilot from utilising the 260 BHP available in order to reduce the possibility of an over pitching accident?
Not being aware that the power margin above 225 BHP is available and should be used to prevent the accident. It’s actually one of the reasons for having a de-rated engine behind you so a ‘get you out of jail free card’!
Not being aware of the need to keep the rpm in the green! Because if the pilot does not keep their rpm at the 102%, then maximum power will not be available (10% less rpm = 10% less power available).
Not having the manual throttle manipulation skill set to be able to instinctively react to reduction in rpm via audible change in engine sound then later the low rpm caution system activation and having to lead (open) the throttle at high power settings in order to maintain their rpm.
This being due to the correlation between throttle and collective pitch setting, under compensates the throttle at high power demands.
There is too much reliance on the engine governor because there is very little useful governor off training either during the basic training and then subsequently during the annual proficiency check (PC).
In general instructors and examiners seem to be scared of turning the governor off!
The younger generation forget we flew the product without a governor for years and we will carry on reminding you for some years to come!
Not being aware that the effect of the stress associated with the situation that the pilot finds themselves in, will cause a physiological response ‘fight or flight’ and one of the effects will be the pilot unwittingly gripping the throttle and overriding the governor’s slipping clutch assembly, preventing the governor from maintaining the rpm when he raises the collective lever.
Thus the rpm decays and as a direct consequence the power available is compromised and the aircraft will sink…as it did!
Given that the OAT and dew point were reported as +8° C and +5° C respectively, this would put the likelihood of carburettor icing in the serious icing area at any power setting.
So, we should not discount this during any discussions and it should be understood that the fact that the R44 carburettor assist system only applies heat correlated to the amount of the reduction of the collective lever, therefore, is not necessarily going to prevent engine power issues due to any accumulated ice that may already be in the carburettor.
Only the application of full carburettor heat by the pilot prior to any reduction in power would clear any ice accumulation.
One further point for discussion on the power available/over pitching element
The amount of disc coning is a good visual indicator for low rpm and over pitching.
The lower the rpm, the more disc coning. The video of the accident does not show any great disc coning at the point of loss of control.
How do we learn from the above?
By acquiring greater system knowledge, training and evaluation of manual throttle skills during the PC.
I mention later in this article the CAA’s own advice on the subject of rotor rpm control published sometime ago.
The next area I would like to consider is the rapid right yaw at the point where it appears that the pilot is attempting to establish a hover.
The report mentions and the video indicates that the R44 yawed right through 180° before striking the ground.
The report gives a good description of the consequences relating to the efficiency of the tail rotor during an over pitching event of the main rotor.
However, there is another possible cause of the right yaw that might be worth considering:
As the pilot’s work load increases due to his approach to a hover rapidly becoming unstable, he was slow or did not apply sufficient left pedal when raising the collective lever.
This allowed the aircraft to start to yaw right.
Tail winds are a yaw rate accelerator and this characteristic comes from the fuselage and vertical fin.
If a yaw rate is established in any direction, in this case to the right with the relative wind from between 120° and 240°, then the yaw rate will accelerate as the aircraft weather cocks into wind.
The pilot stated that the sudden onset of yaw to the right was so rapid that he was unable even to attempt any correction before striking the ground.
With a circa 14 kt tail wind this would certainly be the case, unless the pilot had anticipated this possible condition, which he hadn’t because he thought he was approaching into wind.
Just a point to consider: many years ago I was researching ‘loss of tail rotor effectiveness’ and on one of my annual visits to the RHC factory I had the opportunity to explore the R44 tail rotor authority/effectiveness with their test pilot at ever lowering rpm. We still had good tail rotor authority right up to the point where the R44 would not remain airborne.
How do we learn from the above?
Pre-flight planning.
In the days of long hot summers and crispy bacon we did not have the benefit of all the technology that is available to the pilot today.
I am not going into the whole list of points to be considered when planing off airfield landings, just the basic points.
- Google maps (GM)for example.
If the pilot intends to land off airfield (confined area) they should find their intended landing area on GM and print it out.
Using this tool they can produce a detailed plan of their best approach based on obstacles, particularly wires, include the forecast wind strength and direction onto the picture etc.
- Mark your circuit out with key visual points, including a check power available point.
The first approach is always to a go around, looking for decision height, a safe escape rout out, a second check of power available.
You need a minimum of 1 inch of manifold pressure in hand to effect a go around etc.
This will certainly reduce the pilot’s workload on arrival and lessen the likelihood of misreading the wind direction and being overwhelmed by events etc.
When I was teaching confined area exercises, very often the student would misread the wind direction and 9 times out of 10 it would be a 180° error.
- Improve your knowledge of the effects of different relative wind directions on yaw controllability.
My website: www.morningtonsanfordaviation.com has a good article on ‘loss of tail rotor effectiveness’.
When entering a confined area the wind direction can change suddenly due to the effects of tree lines, buildings etc. and this needs to be anticipated.
Apparently in todays world (which I no longer understand) the examiner is actively discouraged from evaluating the pilot’s confined area and governor off skills during a PC!
This despite a reference made to a CAA Safety Sense Leaflet 17 in the said accident report, which advises the following;
“awareness of the importance of maintaining rotor rpm and proficiency at recognising the recovery from low rotor rpm conditions, both with power on and with power off.”
How do you cover this during training and PC’s if you don’t switch the governor off?
Never mind, the powers to be have made great strides into helicopter flight safety by changing ‘airmanship’ to ’threat and error management’ (very PC!) and changing the ‘down wind check’ to ‘the approach check’!
All of the excellent referenced material in the accident report should be read, discussed and fully understood. A lot of this valuable information is generic to all helicopter types. We are very privileged to have the AAIB at our backs producing these very comprehensive reports. I’m not sure they get the appreciation they deserve.
So, to sum up…learn from the mistakes of others.
Knowledge is flight safety helping to keep your rpm in the green.
This is a tea and biscuit production®
Richard
