The “Standard Spin Recovery Technique”

 

Recovery Use standard recovery technique. Recovery is almost immediate.
Approved Flight Manual & Pilot’s Operating Handbook Airtourer


This rather benign statement describes how to recover from a major killer in aviation. This is not a criticism of the current Flight Manual as it is copied exactly from the original Pilot’s Handbook. Nevertheless, such an important emergency procedure requires amplification.

When the Airtourer was introduced it replaced aircraft such as the Tiger Moth and Chipmunk and spinning was a well established part of the training syllabus. Since then manufactures have made aircraft spin resistant and in many cases intentional spinning is prohibited. As a result a lot of spin knowledge previously accepted as normal airmanship has been lost and the term “Standard Recovery Technique” is no longer appropriate. There remains confusion regarding stall/spin behaviour and recovery techniques so it is worthwhile to look at the historical development of spinning before attempting to determine the standard technique.

All aeroplanes can be made to spin if abused badly, those that claim to be spin-proof are usually limited so that they cannot be abused badly enough. This is the case of the Airtouer as discussed in other articles in this current Newlsetter.

Each aircraft type spins differently and in some cases a standard technique is not appropriate nor will some of the following discussion apply to all aircraft. In these cases very specific spin information and recovery techniques will be provided in the Flight Manual. Unfortunately human factors can come into play and the well established behaviour of reverting to previous knowledge under pressure can lead to use of incorrect techniques. A friend of mine experienced this on pilot’s course when flying the Macchi jet. On a solo handling sortie a stall turn did not work out and resulted in a spin. The Macchi required the elevator to be placed neutral as part of the recovery procedure but when the spin did not recover in the expected time the pilot reverted to the technique learned months earlier on the CT4 and placed the column full forward. The minimum ejection altitude, out of control, was 10,000ft so when he saw the altimeter rapidly unwinding past 7,000ft he pulled the ejection seat handle and lived to tell the tale. Subsequently it was determined that the Macchi entered an inverted spin from the mishandled stall turn and full forward column prevented it from recovering whereas the correct position of neutral would have eventually been successful.

One of the earliest documented procedures was published in Practical Flying of 1918, which quoted “placing the controls – rudder and stick – central”. This will work for many aeroplanes currently flying but was inadequate for many of that time where two distinct control movements were required. The National Advisory Committee for Aeronautics (NACA) was the predecessor or the current NASA and provided extensive information and advice to the aviation community. In it’s Technical Note No 555 Procedure (1936) it advised:

  1. Briskly move the rudder to a position full against the spin.

  2. After the lapse of appreciable time, say after at least one-half additional turn has been made, briskly move the elevator to approximately the full down position.

  3. Hold these positions of the controls until recovery is effected.

There are some very important points in this advice. Firstly the rudder input should not only precede the elevator but there should be a pause between the two. The primary purpose of the rudder is to check the yaw rate, in doing so the nose of the aircraft should go down and the elevator become more effective. On many aircraft, and to a limited extent the Airtourer, the elevator shields the rudder with the stick full forward (elevator full down). Delaying the application of down elevator increases the overall effect of the rudder. On the Airtourer the rudder is mostly forward of the elevator however when held full up the vertical vane that extends into the tail cone will provide an additional surface similar to the rudder.

The rudder input should be brisk, the Technical Note goes on to state, “In certain cases it has been found that, with a slow and cautions reversal of the rudder and elevator, spinning will continue indefinitely; whereas brisk operation of these controls would have effected recovery”.

World War II saw rapid development in aviation. Powerful engines with large propellers and their associated gyroscopic effects introduced new influences into spinning characteristics. The 1943, Cadet’s Handbook of Elementary Flying Training, advised the following:

  1. “…apply full opposite rudder…with your full strength..”

  2. “…when you see that the rotation has practically stopped, press the stick forward….”

  3. “…and finally ease off the rudder…”

Again the emphasis on rudder to oppose the rotation and then elevator to unstall the wings. It goes on to include an emergency action of, “Throughout, always keep full opposite rudder applied”, then describing use of elevator and power to rock the aircraft out of the stall.

 

Later the RAF Manual of Flying Vol. 2 introduced a step to keep the ailerons neutral. Ailerons can be a powerful influence on the spin characteristics, the actual influence depends on their effectiveness in the conventional sense and the balance between the aerodynamic and gyroscopic effects. On high performance jet aircraft where most of the mass is in the fuselage the gyroscopic effect is such that outspin aileron can pitch the aircraft from an erect to an inverted spin. I experienced this at ETPS on the Hawk and the Hunter, only one of them intentionally! The RAAF experienced some cases where the CT4 was reluctant to recover from a spin and inadvertent application of small amounts of aileron was suspected to be the cause. The CT4 has a marker stripe on the instrument panel for alignment of the control column to ensure ailerons are neutral.

One recurring theme in the various recommended spin recovery techniques was the possibility of the spin taking some time to recover. The NACA Tech. Note states:

 

“It is not uncommon for a bad-spinning airplane to make at least 5 turns before the recovery control begins to give any satisfactory results…. In the event, then, of a vicious spin, a rule of great importance is to hold the controls applied for recovery for at least 5 turns before attempting any other measure to promote recovery.”

 

Over time we have seen a gradual development in the awareness of the different influences of various controls on the recovery from the spin. The initial use of rudder and elevator progressed to the interrelation of the two and the importance of rudder blanking and the requirement to counter the yaw rate before unstalling the wings. Later, propeller effects and the use of aileron were introduced and finally the acknowledgement that a spin could take many turns to recover.

 

The most recent authoritative standard recovery procedure I have found was published by the UK CAA in the British Civil Airworthiness Requirements, paper No. K711 dated 9th April 1991.

 

Standard recovery procedure is as follows:

  1. Close throttle;
  2. Centralise ailerons;
  3. Apply full rudder to oppose yaw rate;
  4. Pause;
  5. Push the control column forward as necessary until rotation ceases;
  6. When rotation ceases, centralise the rudder and recover from the ensuing dive.

So where does this leave us in answering the original question of what is the “standard technique” for the Airtourer. From my experience the UK CAA procedure, which incidentally was the same procedure I was first taught on the Winjeel, will work. However simpler techniques will also work on the Airtourer but if it is being used to teach spinning a case could be made to use the standard procedure as listed above.