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Comment by t0mas88 | Hacker News Reader

> Kvochur immediately selected full afterburner for the good engine, but at only 180 km/h (111 mph) he had insufficient rudder and aileron authority to counter the thrust asymmetry and the result was inevitably an irrecoverable departure.

Multi-engine aircraft have a known minimal control speed, below the speed you cannot maintain directional control in case of an engine failure with full power from the other engine.

The theory is that you can only be below that during the takeoff roll and in case of a problem you have to abort the takeoff (close both throttles) to maintain control.

I've never flown military jets, but I expect they have this same concept. Then going full afterburner while below minimum control speed is what put him in an uncontrollable roll.

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> The theory is that you can only be below that during the takeoff roll and in case of a problem you have to abort the takeoff (close both throttles) to maintain control.

During takeoff, or while performing a high alpha/low speed pass showing off the aircraft's unique high-alpha capabilities in an airobatics display. Closing throttles would have been little more than a way to select the area of impact. Considering how close to the central axis the engines are in twin fighter jets going full throttle was probably the least bad attempt to save the plane.

Not just the area of impact but also the attitude then being an upright “normal” landing attitude as opposed to flying it into the ground upside down. So even for an ejection it would be better to close both throttles to keep the aircraft under control and the seat traveling upwards to give you the best chances.

Could thrust vectoring have saved the day, could eg. a Su-35S recover from a similar situation?

Purely speculation, but I had been wondering about this myself before posting: only if the thrust vectoring included considerable yaw authority. And I'd be surprised if typical designs did, because outside of low-speed engine failure situations (or hypothetical "hover on the tail" maneuvers, spacex style) you just never run out of yaw control. While pitch and roll control fall into the category of "more is always better", yaw control has a sufficiency threshold beyond which adding more has little or no use.

> The theory is that you can only be below that during the takeoff roll and in case of a problem you have to abort the takeoff (close both throttles) to maintain control.

Or landing. A famous case is the death of Kara Hultgreen, who suffered a compressor stall and subsequent asymmetric thrust while trying to land a F-14 on an aircraft carrier.

https://en.wikipedia.org/wiki/Kara_Hultgreen#Death

A yes, for fighter jets on a carrier that’s an issue because they have a high power setting while landing. For civilian aircraft the only high risk during landing is a single engine approach with a go around. You go from idle to full takeoff power, at low altitude and speed, creating serious yaw. It is a standard maneuver in recurrent training, but still in reality it would of course be a lot more stressful.

Those cases are eerily similar in how both pilots immediately selected full afterburner before ultimately ejecting (or being ejected). Hultgreen just did not survive the ejection.

From the Wikipedia article:

> The radar intercept officer in the rear seat, Lt. Matthew Klemish, initiated ejection for himself and Hultgreen as soon as it was apparent the aircraft was becoming uncontrollable. First in the automated ejection sequence, Klemish survived. However, by the time Hultgreen's seat fired 0.4 seconds later, the plane had exceeded 90 degrees of roll, and she was ejected downward into the water, killing her instantly.

It seems that she was just 0.4 seconds too late, otherwise she could have survived like Klemish.

> It seems that she was just 0.4 seconds too late, otherwise she could have survived like Klemish.

Well, the plane was. When either co-pilot or pilot ejects, the other is ejected as well shortly after (on pretty much all planes). The delay is likely there to make sure it goes smoothly.

Ejection motors are powerful. You don't want to eject into the fire of somebody else's rocket and since you have no guidance system a simultaneous ejection would just be asking for a collision. Thus a delay is necessary in a front/back situation. (You could build a system for side-by-side simultaneous ejection, design the seats to fly a little to the outside.)

Unless I’m reading this incorrectly, it sounds like she simply got into a skid after trying to overcorrect on final. This is one of the BIG no-no’s in flying, it gets a lot of people killed every year. Sounds like skids were especially dangerous in a Tomcat since they disrupted airflow to the inside engine. I only read the Wiki but it sounds like pilot error. Sad either way.

Retired naval aviator Ward Carroll did a deep analysis of the Kara Hultgreen mishap for anyone interested in the details.

https://youtu.be/rFUXshaaMQM

I wonder what would happen if the pilot did an immediate 90 degree roll to put the good engine under the centreline and then went full throttle?

That would create an even more unstable situation. The training on the civilian side in case of Vmc roll is to close both throttles and rapidly decrease pitch attitude to regain control and airspeed. If you’re lucky to be high enough you can then use power to fly out of it. Otherwise it’s at least an upright / forward crash landing so that’s more survivable. But we don’t have ejector seats :-)

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