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What is the correct procedure in case of vertical stabilizer failure in cruise?

Am I correct in guessing that one should descend to a lower altitude and decrease speed?

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    $\begingroup$ Hi M BA, I will edit your question to add a bit of clarity. Next time, please consider being a bit more clear by writing some more details. $\endgroup$ – Federico Sep 24 '18 at 10:48
  • $\begingroup$ I do not understand your query..can you hint at what more I need to add? It is a very unambiguous question to me. $\endgroup$ – M BA Sep 24 '18 at 12:29
  • $\begingroup$ Please have a look at how I edited your question. You'll notice that I have used a bit longer sentences, this helps with clarity. What you could add, for example: what prompted your question (e.g.: are you studying an accident report?), where have you looked for an answer, why is your guess exactly that. $\endgroup$ – Federico Sep 24 '18 at 12:37
  • $\begingroup$ "correct abnormal procedure" what!... should be "what is the correct procedure". $\endgroup$ – jwzumwalt Sep 26 '18 at 20:39
  • $\begingroup$ Removal of 'abnormal' and previous edits make this question ok. $\endgroup$ – Pilothead Sep 26 '18 at 20:50
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There is no procedure, generally a vertical stabilizer failure makes an airplane uncontrollable, meaning everyone dies. There have been examples where vertical stabilizers failed and people survived, see this question for details. A pilot local to me cut 2/3 of his vertical stabilizer on high tension power wires while scud running and still landed safely.

When there's any control surface failure pilots will have to learn how to fly the airplane and control it using whatever means possible. Differential thrust and speed brakes have been used to control lateral movement (yaw), trim can be used if controls are seized, etc.

Reducing speed may not be a good idea, or at least not all at once, if the vertical stabilizer fails airflow over whatever stump remains may be the only think keeping it straight. If the control is stuck then reducing speed would make sense, it all depends on the nature of the failure. Descending is absolutely a requirement, you have to land somewhere after all, but unless you've depressurized there's no need to rush it, you'd want to work the problem and find out what the new parameters are, then gingerly work your way down.

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    $\begingroup$ Most likely, you'd want to retain as much altitude as possible (while retaining enough O2 to live & think) while trying to figure out how to control your crippled plane. More altitude = more time to live. $\endgroup$ – FreeMan Sep 25 '18 at 14:42
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    $\begingroup$ Well, it all depends @FreeMan, once I figure out how to fly it I'd probably want to get it on the ground sooner rather than later at a facility with the best emergency services and most into wind. The condition of the airplane could deteriorate, and pilot fatigue is a consideration as well. I wouldn't keep altitude just for the sake of it. $\endgroup$ – GdD Sep 25 '18 at 16:30
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    $\begingroup$ @FreeMan: Flying low increases damping, so low and slow is really good advice, especially with swept wing aircraft. $\endgroup$ – Peter Kämpf Sep 26 '18 at 20:42
  • $\begingroup$ Obviously not a pilot... My thought was that the more room there was between you and the ground the less chance you had of contacting it in an uncontrolled fashion while trying to figure out how to control what's left of your aircraft. I yield to those with much greater knowledge who indicated my assumptions were incorrect. $\endgroup$ – FreeMan Sep 27 '18 at 11:17
  • $\begingroup$ That's a common thought @FreeMan, and it is right in some situations but not all of them. $\endgroup$ – GdD Sep 27 '18 at 12:04
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Am I correct in guessing that one should descend to a lower altitude and decrease speed?

Yes, if you fly an aircraft with a backward swept wing. Otherways, losing the fin will be impossible to compensate.

This answer explains how a backward swept wing will aid in directional stability, and this help increases with angle of attack. Therefore, flying slow is the most important step in order to restore directional stability. Flying low increases aerodynamic damping, so low and slow is the best choice in this case.

@Carlo mentions B-52H 61-023 which lost most of its vertical on January 10, 1964. This aircraft survived, but a number of them who suffered the same fate crashed. There were several factors which helped:

  • Just enough of the tail was left to keep the aircraft flying. Later simulations showed that a full loss of the vertical would had been impossible to compensate.
  • The crew lowered the rear landing gear, so the gear doors helped by doubling as ventral fins. Every bit counted on that occasion!
  • Also, the loss of mass from the lost tail portion shifted the center of gravity forward, which is another way to improve directional stability. The crew did all they could to get the center of gravity forward, and again, without that the aircraft would had lost directional stability.

What is the correct abnormal procedure in case of vertical stabilizer failure in cruise?

My advice: Don't count on being as lucky as B-52H 61-023, but bail out as long as you can!

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Depends on the aircraft. Generally structural failure results in departure from controlled flight, though there are a few exceptions such as this USAF B-52H which lost its vertical fin over Colorado on Jan 10, 1964.

Oddly enough, the loss of a vertical fin is probably the least riskiest form of structural failure. An airplane can still maintain approximate directional control from the longitudinal center of pressure from the tailboom of the airplane well behind the center of mass, provided all other systems remain functional. The airplane can still be turned using aileron input, though slipping and skidding from adverse yaw and other factors are going to be much more pronounced demanding greater care in handling at lower speeds. Multiengine aircraft will most likely depart from controlled flight here in the event of an engine failure. Again the severity of the loss of control here will depend on the amount of structure lost and it’s effect on directional control.

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  • $\begingroup$ For this type of failure, the B-52 has an advantage in that it doesn't have ailerons. It relies entirely on spoilers for roll control. The spoilers deploy on the wing in the direction of the turn, adding drag as well as reducing lift. This generates the roll with almost no adverse yaw. $\endgroup$ – Gerry Oct 5 '18 at 17:50
  • $\begingroup$ Even with a little adverse yaw, it does not necessarily mean a loss of control, you still have quite a bit of surface area from the tailboom to provide some directional stability, though care should be taken - never try something risky in a compromised airplane. $\endgroup$ – Carlo Felicione Oct 5 '18 at 21:43

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