1

A corkscrew approach is an unusual type of approach used in places like BGW/ORBI to minimise an aircraft's exposure to antiaircraft fire on the way down; it involves staying at cruise altitude until one is directly over the airport, then descending to the runway in a fast, tight spiral.

Given that the tight, spiralling descent would seem to make it almost impossible to determine whether the approach is stabilized or not, how does a pilot performing a corkscrew approach make this determination?

Vikki
  • 28,337
  • 16
  • 122
  • 282
  • 1
    I'm not sure why anyone would expect a maneuver like that to be stabilized. Are you asking what the correct technique is? – Pondlife Feb 25 '19 at 06:05
  • 1
    The corkscrew approach still ends with a mostly normal final for the last 500–1000 ft, doesn't it? The term stabilized approach only applies to final. – Jan Hudec Feb 25 '19 at 06:19
  • 2
    Being shot at and stabilized approach seem to be a contradiction (oxymoron)? – jwzumwalt Feb 27 '19 at 08:35

3 Answers3

6

The corkscrew approach as Wikipedia describes it is what the military refers to as a “Force Protection” measure to be used when operating in a high threat environment. It is not a published procedure in the traditional sense of the word, but something that is put in place by the theater commander and briefed to aircrews when driven by the current intelligence assessment of the threat level.

It is not intended to be flown as a precision maneuver like an instrument approach would be. It is a dynamic, eyeballs outside the cockpit looking for a missile, combat visual descent. A high rate of speed is maintained until as late as possible in order to make evasive action possible. Not only is it clearly NOT a stabilized approach, it is actually the exact opposite: Done in VFR conditions, the aircraft isn’t configured until just before landing.

Contrast this with the definition of a stabilized IFR approach from FAASafety.Gov below:

Stabilized Approach Concept. A stabilized approach is one in which the pilot establishes and maintains a constant angle glide- path towards a predetermined point on the landing runway. An airplane descending on final approach at a constant rate and airspeed travel in a straight line toward a spot on the ground ahead.

There is a lot of additional information available about stabilized approaches out there for anyone interested so I won’t attempt a further explanation about the intent. By definition, however, a corkscrew approach is not stabilized.

So, back to the original question: “How does a pilot performing a corkscrew approach make this determination?” (whether the approach is stabilized or not…) The answer is that a pilot performing a corkscrew approach isn’t asking himself those kind of questions. The distinction is completely meaningless.

He/she is looking outside for the smoke trail of a stinger rising from the ground, and working to get the plane to a point where they can pull the nose up to break the rate of descent and slow down, slap the gear and flaps down, and make a tight 180 combat turn to a short final to lessen the exposure time when they are dirty and slow. The goal is to get on the ground as safely and expeditiously as possible and minimize any time spent “stabilized” on a long straight-in approach.

Stabilized approaches are what tactical aviators fly stateside when practicing for their annual instrument proficiency check.

Michael Hall
  • 25,964
  • 2
  • 62
  • 99
6

It is very important to know how much altitude you lose per 360 degree turn. You essentially set up your turn at a given bank angle, say 45 degrees and a safe speed to avoid an accelerated stall. You execute the turn at a lower power setting than a normal steep turn, resulting in a "corkscrew" descent path through the air. If your AGL matches your altitude loss per turn plus enough to roll out for short final, it works.

So if my plane loses 1000 feet per 360 turn at a given bank angle and power setting, I would "approach" at any altitude divisible by 1000, say 10,000 feet AGL to avoid AA. Add 300 feet for roll out, starting corkscrew at 10300 feet AGL and checking altitude every turn.

Note rate of descent is still controlled by power, so by checking each turn (half or even quarter turn) and maintaining bank angle, yes, one could say this was a "stabilized" approach. Your last turn would be very similar to a standard "base to final".

Robert DiGiovanni
  • 20,216
  • 2
  • 24
  • 73
  • 2
    have you ever actually flown a force protection descent to landing in a combat environment? I'm curious because except for disagreeing that it meets the definition of stabilized, there's otherwise nothing technically incorrect in your response. I just feel it lacks a sense of the real purpose... – Michael Hall Feb 28 '19 at 02:52
  • 1
    This is why your response excellently compliments mine. I was focusing on the technique, rather the flying the "L7" pattern. You can stabilize a constant turn at a known sink rate, this is your approach to the airport. The "landing pattern" is a very truncated quarter turn. As with all landings, stepping through the keys correctly increases the chances of a good landing. Power controls rate of descent. No, I am not a combat pilot, but would do everything I could to help get them home safe. – Robert DiGiovanni Feb 28 '19 at 03:59
  • Thanks Robert. You do espouse a good technique. – Michael Hall Feb 28 '19 at 05:53
0

I don't see any published charts there for anything that looks like a "corkscrew" approach. Regardless, each operator has their own criteria for what constitutes a stabilized approach and when the airplane must be stabilized during an approach.

If an approach can't be done while meeting their criteria, then either it won't be authorized, or it will get an exception and require special training.

Khantahr
  • 3,106
  • 21
  • 23