I avoid discussing incipient spins at the same time as fully developed spins to make it quite clear that the recommended recovery actions are quite different.
Let’s see what CASA has to say on the subject in their Flight Instructor Manual.
Chapter 9 Stalling:
“Show that lift increases until the critical angle is reached. ….. Smooth airflow then becomes turbulent and lift is decreased. This is the stalling angle.”
Interesting to note in CASA’s article at http://www.flightsafetyaustralia.com/2016/03/angle-attitude-stallspin-crashes-and-how-to-avoid-them/ that:
“There’s an interesting characteristic of angle of attack in most general aviation aircraft: critical AoA, the onset of a stall, begins at a 17 degree AoA or so, but maximum lift development occurs just before reaching the critical angle of attack.” Hmmm – a different definition of critical angle perhaps?
The Flight Instructor Manual Chapter 9 goes on:
“RECOVERY WHEN THE WING DROPS
Use the standard recovery, i.e. simultaneous use of power and forward movement of the control column. In addition rudder must be used to prevent the nose of the aeroplane yawing into the direction of the lowered wing. The ailerons should be held neutral until control is regained, when the wings should be levelled.”
Unfortunately, some CASA documents refer to this as an incipient spin! It is but it isn’t really!
Chapter 13 of the Flight Instructor Manual is Spins and Spirals. I can’t see a specific definition of incipient spin there but anyway:
“RECOVERY AT THE INCIPIENT SPIN STAGE
Brief the student that you will be demonstrating the entry to the spin in the normal manner. Point out that before the spin develops fully you will be recovering by ensuring the throttle is closed and the controls are centralised followed by recovery from the ensuing unusual attitude.”
But on the following page, in the same chapter:
“RECOVERY FROM THE INCIPIENT STAGE
Carry out the pre-spinning checks. From a straight glide use the controls as for the entry to a fully developed spin. As soon as the aeroplane has stalled and commenced to yaw take the appropriate recovery action. Increase power, apply sufficient rudder to prevent further yaw and ease the control column forward sufficiently to un-stall the aeroplane. Point out that if power is to materially assist recovery action it must be applied before the nose of the aeroplane has pitched too far below the horizon otherwise its use will only increase the loss of height.”
Power can also aggravate the autorotation if the pilot mishandles the other actions.
Let’s see what CASA has published in their CAAP 155-1 Aerobatics: absolutely nothing on incipient spin recovery!
It seems that we must go to the USA’s FAA Airplane Flying Handbook free online at https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/airplane_handbook/ for a definition of an incipient spin. It is interesting that, in Chapter 4 Slow Flight, Stalls, and Spins, they discuss cross-control stalls including a skidding turn which still does not feature in CASA’s documentation.
“During the turn, excessive rudder pressure should be applied in the direction of the turn but the bank held constant by applying opposite aileron pressure. At the same time, increased back-elevator pressure is required to keep the nose from lowering. All of these control pressures should be increased until the airplane stalls. When the stall occurs, recovery is made by releasing the control pressures and increasing power as necessary to recover.”
It goes on to define the incipient spin as:
The incipient phase is from the time the airplane stalls and rotation starts until the spin has fully developed. This change may take up to two turns for most airplanes.”
Then it defines the fully developed phase:
The developed phase occurs when the airplane’s angular rotation rate, airspeed, and vertical speed are stabilized while in a flightpath that is nearly vertical. This is where airplane aerodynamic forces and inertial forces are in balance, and the attitude, angles, and selfsustaining motions about the vertical axis are constant or repetitive. The spin is in equilibrium.”
Quite clear to me!
The APS Emergency Maneuver Training Pilot Training Manual is also a good resource which is free online.
“RECOVERY Stall Recovery (See Exercise #5)
* Power selection considerations will be discussed during ground Training”
This is amplified on their website at http://apstraining.com/the-incipient-spin-recovery/
“STALL RECOVERY PROCEDURE
An example of a stall recovery for most general aviation aircraft and most other aircraft types and classes is as follows:
PUSH: Reduce AOA (forward movement of the control column) to allow the wing to reduce AOA below critical AOA, reduce drag and to immediately transition from stalled fight to normal unstalled flight. Common tendencies are to either over-push causing excess nose drop below the horizon increasing altitude loss or a fore-aft pumping motion of the yoke causing one or more secondary stalls.
POWER: Smoothly add up to full power (usually) to increase airspeed and minimize altitude loss. We can do stall recoveries all day with the power at idle, however, an idle power setting is not assisting us in minimizing altitude loss. Keep in mind that there are certain situations that selecting power to idle in the stall recovery is the proper action. Examples include high-torque single-engine prop aircraft and in a Vmc situation in a multi-engine aircraft.
RUDDER: If there is any roll/yaw motion associated with the initial stall and the wing is still at or beyond critical AOA, the rudder should be used to stop the yaw-roll couple from developing. The amount of rudder used is only enough to coordinate the flight condition and should be accomplished in one application. Pumping or cycling the rudder is not a desirable technique especially for large aircraft. Note that the rudder is not used to roll the aircraft wings-level in a stall recovery. Common errors in the use of rudder vary from not using it all to using it far too much, for too long. Rudder is critically important in an uncoordinated stall condition (such as a cross-controlled stall) to ensure the stall is not allowed to develop from a stall to a spin.
ROLL: When the wings are clearly unstalled and coordinated flight has been regained. The aircraft’s flight attitude must be immediately be re-oriented to a wing’s level condition by rolling with aileron and coordinated rudder to the nearest horizon. Again, the aircraft should not be rolled by use of rudder alone at this stage. The primary roll control in normal flight is through the proper use of ailerons.
CLIMB: With the wings level in coordinated flight, aft yoke movement should be immediately applied to initiate recovery to a climbing attitude. The amount of elevator movement applied must ensure the aircraft remains below critical AOA at speeds below Va and at a load less than the limited load factor of the aircraft at speeds above Va.
Essentially, the first three steps of the stall recovery (1-2-3) are directly focused on safely recovering the aircraft from the stall and the last two steps (4-5) are to recover from any resulting unusual attitude. It is important for the pilot know and understand that these processes can not be successfully reversed. The stall must be solved first, regardless of the flight attitude of the aircraft, then followed by solving the unusual attitude.”
CASA’s recovery technique from a stall with a wing drop is fine for the usual practice straight stalls but note that rudder is really superfluous as forward movement of the stick will unstall the wing and the dropped wing can then be easily rectified with aileron. Some of you may be aware that aircraft certification requirements mandate use of the aileron for roll control at the stall – but note that is only for aircraft certified in recent years – we still fly many aeroplanes which were NOT certified to those requirements. Mishandling at the stall, say the classic skidded turn at low height, is quite different however in that the entry to the post-stall gyration is much more aggressive – this is the one that everyone should be wary of and know the immediate correct actions for recovery. Messing up an aerobatic manoeuvre is a similar situation although the altitude is generally higher.
The Super Decathlon is an example of a type certified to an older version of FAR 23 and it has this statement in the Operating Manual:
“The Super Decathlon stall characteristics are conventional. The stall warning horn will precede the stall by 5 – 10 MPH depending on the amount of power used. There is very little aerodynamic buffeting preceding the stall.
Aileron control in a power on stall is marginal. Large aileron deflections will aggravate a near stalled condition and the use is not recommended for maintaining lateral control. The rudder is very effective for maintaining lateral control in a stalled condition with the ailerons placed in the neutral position.”
An inadvertent stall/spin entry requires immediate action to unstall the wing and to remove the aggravating control deflections. Move the stick forward and get rid of aileron and rudder input. In other words:
Centralise the controls.
If you are in something like a Pitts then it is essential to close the throttle – reduction of power tames this aeroplane. If in something more docile then power is a secondary consideration so initially don’t need to do anything with the throttle. If centralising the controls doesn’t have an immediate effect then you are on your way to a fully developed spin so remember those actions from my other article – the first action is power to idle so this is the time – do it now. If centralising controls is having a positive effect then you now get to decide what to do with the throttle.
Consider the accident to a Cirrus in NSW in May 2014 – the ATSB report is at https://www.atsb.gov.au/media/4920573/ao-2014-083_final.pdf
“The PIC then took control of the aircraft and stated ‘watch this’. He selected 50% flap, rolled the aircraft into a left turn at about 25° angle of bank, reduced the power to idle, and raised the nose of the aircraft. The passenger in the front seat queried the use of flap and the PIC confirmed it was intended. As the aircraft approached the stall, the PIC pointed to the vertical speed indicator. As he did this, the right wing dropped rapidly and the aircraft entered a spin to the right. The PIC reported that at this time he performed his normal recovery procedure from this manoeuvre: maintained a neutral aileron control position, applied forward pressure on the control stick to pitch the aircraft nose down, rudders neutral and applied power. He reported that he moved the throttle lever forwards to increase power however there was a distinct hesitation in the engine response. The passenger in the front seat reported that on about the third rotation of the spin, the PIC said ‘I’m sorry’ ……….”
So, the pilot responded to the post-stall gyration by centralising the controls and applying power however the autorotation continued to develop into a spin. Application of power can have a significant adverse effect and aggravate the post-stall gyration. Reduction of power will eliminate that aggravating effect. If you know that application of power will not make the situation worse and you think it will reduce the height loss then by all means do it – but be absolutely sure that you are correct. Of course, this particular pilot had a parachute to recover the aircraft so a better option earlier on.
Finally, it is very important to know how your particular aeroplane type behaves at the stall. What is the best thing to do in the type that you normally fly if you inadvertently start to spin at a low height? You must also consider your own experience and level of competency. How will you react if the aeroplane suddenly departs controlled flight at low altitude? It is all very well to know of a procedure to recover with minimum height loss but of little use if you mishandle the procedure and make it worse instead with application of power. A typical situation is the forced landing approach following an engine failure when your stress levels are already very high. Of course, in that situation, you don’t have power available to you anyway. APS has identified these common reflexive actions in initial stall/spin training – so, if a spin is suddenly encountered with nil training then expect one or more of these to occur which will make life much worse. e.g. “• Involuntary swearing and sweating • Continuing to hold the elevator control aft because of a dramatic, nose-down flight attitude • Inadvertently applying opposite aileron as a wing dips at the stall break, or as the airplane starts to roll into an incipient spin • Wildly shoving the elevator control forward”.
The bottom line, in my opinion, is to remember this set of immediate actions for recovery from an inadvertent spin entry:
- Centralise the controls
- Close the throttle
- Recover from the ensuing unusual attitude