That aircraft had aluminium side panels added at some point, which if down at the same time as the MT prop might explain the CG/weight change when the aircraft was re-weighed. They aren’t mentioned in the report so I imagine they were added at the same time. I used to have a share in a similar aircraft that had the side panels added, and although I sold it before the work was completed, we had expected it to add about 10 kg. Reading the report though, I don’t believe any of the mods or the W&B had any bearing on the incident at all. That aircraft had be flown extensively in that configuration for a long time without incident.
As to wearing parachutes, they are quite cumbersome in small cockpits, and very fiddly when worn under an aerobatic harness. The idea that you can get out in a hurry to actually make one useful in the time available is certainly debateable. I wouldn’t like to attempt it.
I know from my experience, that subsequent spins tended to make me feel progressively green, which didn’t do anything for my responsiveness. The report doesn’t seem to consider this, or the potential for the instructor to be exhibiting audible/visual distress, or the volume of the aircraft and the headsets used. I had quite a bit of trouble with effective communications in the Pitts even with an ANR helicopter headset.
It is a sad thing to read about. I feel bad for all involved.
I would not over interpret the accident and/or the report:
In this situation there has been 17 seconds between start of the spin (where everything has been still normal) and the last chance to act to avoid the accident. If the FI got incapacitated let’s say 5 Seconds into the spin, there have been 12 seconds left for the other pilot to react.
12 Seconds to a) figure out that something is actually wrong b) figure out, what is going wrong c) decide, what to do now and finally d) actually do it. This is an extremely short time for all of this.
In the end, it just looks like an extremely unfortunate (and unlikely) event at the worst possible moment in time. An “accident” in the original meaning of the word…
RobertL18C wrote:
Not sure how much weight difference there is in the two propellers, possibly a few pounds (2 or 3).
Probably the MT is 13 pounds lighter than the Hartzell for a Lycoming 360, depending upon MT model. My MT is heavier as it’s a reversing model.
Certainly if informed opinion is that the empty CG in that latest M&B seems highly unusual for the type, then it is probably worth raising it with the AAIB. As you say, never trust someone else’s arithmetic. Looking at the revised M&B chart in the report, it begs the question of how one is supposed to actually load within limits and thus suggests something may be wrong somewhere.
They do not say how they verified that 64 litres of fuel was onboard at takeoff. They also don’t say how they assured themselves that the version of the spreadsheet they found on the commander’s computer was created for that particular flight. I keep similar on my computer and if someone came looking at it after the event there is no way to verify to intended use of the data that might be found in it – I might have saved it after the last time I used it, or I might not. The best clue would probably be the ‘last accessed’ date stamp that File Explorer puts on the file, but that still doesn’t verify the intended purpose of that set of numbers.
In the reproduction of the commander’s spreadsheet they are right on the line with 64 litres of fuel, and it takes the also-reported significant under-estimate of the crew weight to achieve that.
In the Pitts, only fuel is ahead of the empty CG, and it is flown from the rear seat. This example had flown for years with the MT MTV-9 three blade composite propeller. This had replaced a two blade metal Hartzell. Not sure how much weight difference there is in the two propellers, possibly a few pounds (2 or 3).
I can confirm from direct experience that spin characteristics in this example were viceless, both standard or accelerated (flat), with the CG further back than in the accident flight. I find the revised M&B following the propeller change to be in need of checking. M&B schedules are notorious for the most basic of arithmetical errors, and if the operator had known about the new M&B am sure they would have investigated it. Moving the empty CG aft by 1.79in meant that it would only be in the aerobatic envelope flown solo.
Pilot_DAR wrote:
When you push the stick full forward, and the nose does not come down as expected, and perhaps increased drag from an idling prop changed the airflow over the tail. This was certainly a factor in one of my planes, when I changed from a Hartzell two blade to an MT three blade, the airplane have much less favourable glide characteristics
I imagine 3 reasons why prop change makes a huge difference in spin:
1) Assymetric & P-factor: small but adds more glide drag it’s not good for spin and very pronounced when engine is still running
2) Propwash & elevator authority: not entirely sure but the impact on glide should pass-through to elevator airflow & authority
3) Weight impact on GC: I think this is obvious
I am sure a certified aircraft withing GC limits should be able to get out of stall/spins while engine off or idle (the one that can’t has BRS/CAPS), I still hope that losing it’s prop while under GC limits and suddenly out GC limits at high AoA is recoverable with elevator & rudder only, but I can only confirm from few YT aeronbatics videos where aircraft was dragged on prop before losing it, all of them end up well with forced landing but those pilots had +10,000h in Extra300s…
But I can see why a light weight 3 blades prop turning does make spin exit more tricky as adds to assymetry, drag and aft GC !
RobertL18C wrote:
One odd conclusion is around the M&B. The aircraft had a new MT propeller fitted which increased the empty weight by around 27 lbs, but moved the empty CG back by a significant margin. At first reading this doesn’t make sense, unless the new propeller weighed considerably less (moving CG aft) and the increase in empty weight was due to the usual weight gain (new paint or avionics which sit in the rear, but it only had Trig com from memory), with age. Ideally the AAIB might have been more careful before saying it was being operated out of envelope. The revised M&B just doesn’t look right.
I read that part as the AAIB hinting that they thought the old M&B was of dubious provenance and probably had not been correct for the aircraft for some time, if it ever was at all. Hence the reference to a “like that when I found it, guv” answer from the operator.
johnh wrote:
180 lbs (82kg) is about the lowest weight for a normal American male (e.g. my acro instructor, who is 6’ and pretty slim). With two of those you can take enough fuel for about 15 mins of flight. Make it 200 lbs – typical weight of an adult US male – and you can’t even fly round the pattern twice. Much the same for the 152.
I think that says a lot about how the population has changed since these aircraft were designed. 82kg is 13 stone (and is 2 stone more than I weigh) and you call that the minimum for an American adult male…. I guess people are both taller and fatter than they were 50-60 years ago. Personally I work on the basis that all W&B bets are off whenever anyone ‘big’ is involved – it must be calculated, and with real weights not wishful-thinking ones – and generally I don’t take people bigger than a certain size (say probably around 82kg – unless they are quite tall) flying with me because they are liable to be spilling out of their seat and I’m not keen on that. On the UK GA scene one does see a lot of people who are evidently W&B nightmares, including plenty of instructors.
If an MT three blade replaced a metal two blade (I don’t know, just speculating), there will be a W&B change, and possible effect on the power off glide characteristics. we often choose an MT prop to reduce a nose heavy effect (particularly Cessna floatplanes). A tail heavy airplane will usually seem nicer to fly and be a little faster, because less tailplane downforce is required. However, a C of G behind the aft limit might make a spin much more difficult to recover, and startlingly so. When you push the stick full forward, and the nose does not come down as expected, and perhaps increased drag from an idling prop changed the airflow over the tail. This was certainly a factor in one of my planes, when I changed from a Hartzell two blade to an MT three blade, the airplane have much less favourable glide characteristics.
I trust that the AAIB considered this in their report, and their remarks about behind the aft limit seem clear to me. Pilots need to consider aft C of G errors with great seriousness, particularly for spin recovery.
The floor was 1500ft agl and you do max 1.5 spin from 3000ft which is way more than enough but in congested airspace not ideal for an-initio training or instructor incapacitated, if aircraft is out of balance, the height at which the spin starts may not matter much…
I agree with Rob, the revised W&B is just odd (a bit like saying an aircraft losing a heavy prop will pitch up stall too early and go into unrecoverable spin?)
RobertL18C wrote:
The flight was an early sortie in teaching aerobatics at the Sports level. This will have an extensive brief, with the instructor teaching a walk through and planning a sequence in a competition box. At Sports, the floor of the 1 km cube box is 1,000 feet AGL, and spin entry in a sequence is toward the upper limit of the box.
This is exactly as I would have expected, and i am sure there would have been a thorough brief.
Ultimately it maybe as simple as surmised earlier – unfortuantely the instructor had a medical event, the student did not realise, and did not initiate a spin recovery. Unfortunately sometimes it is this simple, and a chance in a million.
The student may simply have not had the experience to realise the spin should have been recovered, or maybe it was his recovery but he was disconcerted by the added pressure on the controls caused by the instructor’s medical event.
Sometimes we can only speculate, and with these incredibly rare events even the ebst brief may not provide the solution.
