Aircraft crashes - pilots averting bigger disasters

A helicopter crashed yesterday after a Premier League game. It’s looking likely the tail rotor failed. The papers here are reporting the pilot steered away from the crowds and averted a much bigger disaster -

How much control would the pilot have in this sort of situation?

Pretty much zero from my (admittedly limited) understanding of helicopters. Without a tail rotor you can’t keep it pointed in the direction you want to go.

Which is not to say the pilot didn’t try to minimize casualties, I just question how effective such action would be under those circumstances.

There have been a number of aviation accidents where the pilot(s) really did take action to limit the danger to those on the aground. There have also been a number where this was claimed but in fact the pilot had no control and it was good fortune no one on the ground was killed. It can be hard to tell until after the official inquiries are completed.

This is actually possible. If the helicopter has enough forward airspeed (close to cruising speed) when the failure occurs, and depending on the helicopter design, the vertical stabilizer may provide enough directional control to allow the pilot to maneuver the helicopter to a more desirable landing sight.

In English, it means that if the helicopter is going fast enough it can still use the fins on its tail to adjust the direction it is flying. Or rather, crashing.

If a helicopter has a low airspeed or is in hover, odds are that it will begin to spin out of control. In this case, all the pilot can do is reduce throttle and hope it lands somewhere soft.

What helicopter has controls that affect “the fins on its tail” independent of the tail rotor?

Yes - with plenty in the latter category.

The “hero pilot who nobly steered away from the crowd” is a meme that appears frequently in the aftermath of accidents, seemingly with little need for actual evidence. To the extent possible, pilots will quite naturally head for open areas when a crash seems imminent; self-interest is sufficient motivation for this.

Not really. While the fin does have some effect on direction in cruise flight, it is pretty much useless in the event of a tail rotor failure. The tail rotor is properly called the anti-torque rotor, and exists to counteract the torque of the engine and main rotor. If it fails, the helicopter will spin. The emergency procedure is to chop the power, which removes the torque, which stops the spin. Engine power may be used to extend the glide in certain situations, but this will induce the yaw again. You can still turn with the cyclic, but your yaw control is out.

There is a procedure for autorotations when hovering a few feet off of the ground, and the helicopter will not spin out of control.

Let me refer to the Height-Velocity Diagram, aka ‘Dead Man’s Curve’. You need to have some airspeed to initiate an autorotation. If you’re hovering, you trade altitude for airspeed. If you’re in the shaded area on the left side of the HV diagram, you won’t have enough altitude to buy enough airspeed for a successful autorotation.

Helicopters often operate out of confined areas. In training, my instructor said it’s a calculated risk. If you need to operate out of a confined area, you take your chances – but chances are excellent nothing bad will happen. In the case of the stadium crash, the pilot simply didn’t have enough altitude or airspeed to recover from a tail rotor failure in a confined area. (NB: Tail rotor failure may be a mechanical fault, or it could also be that the pilot struck an obstacle.)

To add one thing to Johnny L.A.'s excellent account: when you have to climb steeply out of a confined area at low airspeed, inside the “dead man’s curve”, it’s much safer to be in a twin engined aircraft - which this was, an AW169. This protects you against actual engine failure.

Unfortunately, that doesn’t help you with a tail rotor failure. When the tail rotor fails, you must cut engine power immediately to eliminate torque, otherwise the aircraft will spin. In other words, the escape strategy from a tail rotor failure is to simulate engine failure and enter autorotation immediately. So however many engines you have, you must cut power immediately or spin.

(Johnny, I’m sure you know this and just slightly misstated it, but to clarify for other readers…)

A slight nitpick, you can enter an autorotation with no airspeed. But you need forward airspeed in order to land an autorotation successfully. The end of a successful autorotation is the flare, where you convert forward momentum into a reduced rate of descent.

If you enter a zero-airspeed autorotation with enough height, you can gently ease the nose down and do the reverse of a flare - increasing rate of descent temporarily in order to gain forward airspeed. But you need plenty of height to achieve this safely. That’s why the deadman’s curve slopes back, showing that it’s safe to hover either a few feet off the ground, or more than ~750’ above the ground, but not between.

I thought I mentioned ‘from a hover’, implying that you don’t need airspeed to enter autorotation; just enough height. On re-read, I see that I did not phrase it clearly.

You are correct. If you are hovering at altitude, lower the collective and point the nose down to trade some of that altitude for airspeed. This keeps the rotors turning so that you can ‘glide’ to a safe landing.

If this was a tail rotor failure at a few hundred feet directly above the stands, the pilots probably had no chance. Climbing out at full power, low airspeed, at night, the obstacle of the stadium below… unless you chop power within about a second you are spinning, and even if you do you have no airspeed and probably nowhere to go even if you could see clearly. Helicopters do these takeoffs all the time, it’s what they are designed for, and you stay as safe as possible just by keeping the period in the dangerous flight regime as short as possible. If the worst thing happens at the worst possible time, there’s not always a way out even with zero reaction time and perfect visibility.

Given where it happened, it may turn out that it wasn’t a mechanical failure, perhaps it’s more likely that the tail rotor struck something. But I don’t think we know for sure that it was tail rotor failure yet. Some eyewitness accounts say it was “spinning”, but I’m not sure you can reliably infer what was happening from that.

Low airspeed, high power, sudden loss of tail rotor - this gives a feel for how fast a heli spins.

The pic is a little dark. Did he strike a flag?

Also, are the people still married? (Seemed like an omen! :stuck_out_tongue: )

This video seems to show the helicopter climbing normally to an altitude that’s plausibly above normal obstructions around a stadium. It then (0:52) pretty clearly starts spinning, almost certainly indicating loss of tail rotor anti-torque.