Accelerated Stalls

A stall that occurs any time the G-load exceeds +1G — the AFH calls these "accelerated maneuver stalls" (AFH ch. 5). At a given weight, configuration, CG, power, and conditions, the airplane stalls at the same indicated airspeed at +1G, but under acceleration greater than +1G it stalls at a higher indicated airspeed. Turning, pulling up, or any abrupt change of flightpath will do it.

• Entry altitude allowing completion no lower than 3,000 ft AGL — with no lower single-engine option, unlike Tasks A, B, and C, which allow 1,500 ft AGL for ASEL/ASES and only require 3,000 ft for AMEL/AMES (CA.VII.D.S2)
• Configuration as specified by the evaluator (CA.VII.D.S3)
• Power set so airspeed does not exceed VA or any other applicable POH/AFM limitation (CA.VII.D.S4)
• A coordinated turn in a 45° bank, increasing elevator back pressure smoothly and firmly until an impending stall is reached (CA.VII.D.S5)
• Acknowledge the cues at the first indication (CA.VII.D.S6), recover per the POH/AFM (CA.VII.D.S7), then accelerate to Vx or Vy and return to the assigned altitude, heading, and airspeed (CA.VII.D.S8, S9)

Impending. The skill element stops at "until an impending stall is reached" (CA.VII.D.S5) and recovery is at the first indication (CA.VII.D.S6). Unlike Tasks B and C, the evaluator does not have the option of asking for a developed stall — the ACS Appendix 2 note for multiengine airplanes says the same thing outright: a successful recovery occurs at the first indication of a stall.

Because accelerated stalls are more aggressive than unaccelerated +1G stalls — they occur at higher-than-normal airspeeds and lower-than-anticipated pitch attitudes, and can surprise a pilot into an unexpected attitude where failure to execute an immediate recovery may result in a spin or other departure from controlled flight (AFH ch. 5). The extra 1,500 ft is spin room.

Because VA is the speed at which the wing reaches critical AOA before the airframe reaches its design limit load. Performing accelerated stalls at speeds up to VA (or VO) ensures the airplane will stall — which unloads the wing — before exceeding the design load limit. Above VA, the airplane can reach its design load limit at less than the critical AOA, making it possible to add more load and overstress the airframe (AFH ch. 5).

The design maneuvering speed is the speed below which you can move a single flight control, one time, to its full deflection, for one axis of rotation only (pitch, roll, or yaw), in smooth air, without risk of damage (PHAK ch. 5). VA must be published in the AFM/POH of recently designed airplanes; for older GA airplanes it is approximately 1.7 times the normal stalling speed. The critical caveat: operating at or below VA does not provide structural protection against multiple full control inputs in one axis or full inputs in more than one axis at the same time (PHAK ch. 5).

VO — operating maneuvering speed — is a historical operating limitation applicable to certain airplanes only. It represents the maximum speed at which, at any given weight, the pilot may apply full control excursion without exceeding the design limit load factor (AFH ch. 5). Where your POH publishes VO, that's the number to fly this maneuver at or below; otherwise use VA.

Because of the lower design G-load limitations in that configuration — the AFH says a pilot should never practice accelerated stalls with wing flaps extended (AFH ch. 5). The flap-extended structure is not certificated for the load factors this maneuver deliberately produces.

1.41 G in a level altitude 45° banked turn (2.0 G at 60°) (AFH ch. 10). Stall speed increases as the square root of the load factor (PHAK ch. 5) — the AFH's worked case: an airplane that stalls at 50 knots in level flight stalls at 60 knots in a 45° turn and 70 knots at 60° of bank (AFH ch. 10).

In a coordinated level turn it behaves much like a wings-level stall, except the buffet can be sharper and the nose pitches away from the pilot because both wings stall nearly simultaneously. If the airplane is not coordinated at the stall, expect a change in bank angle until the AOA is reduced (AFH ch. 5). You will also feel the G — the increased back pressure pushes you down in the seat, and the added lift adds drag, so airspeed may decrease during the pull.

Take action at the first indication (AFH ch. 5):

1. Forward elevator pressure as required to reduce AOA and eliminate the stall warning
2. Level the wings using ailerons, coordinated with rudder
3. Adjust power as necessary
4. Return to the desired flightpath — accelerate to Vx or Vy, configure per the manufacturer (CA.VII.D.S8)

Always follow the POH/AFM procedure where one is published (CA.VII.D.S7).

The AFH's list (ch. 5):

• Improperly executed turns
• Stall and spin recoveries
• Pullouts from steep dives
• Overshooting the base-to-final turn

Add the pull-up over rising terrain and the abrupt maneuver to avoid traffic. The thread is a hard pull at a speed that felt perfectly safe a second earlier.

Two are published (AFH ch. 5):

• Most common — from straight-and-level flight at an airspeed at or below VA/VO, roll into a coordinated, level 45° turn, then smoothly, firmly, and progressively increase AOA with back pressure until the stall
• Alternative — roll into the coordinated level 45° turn at a speed above VA/VO, wait for the speed to slow to VA/VO, and then, at 5 to 10 percent faster than the unaccelerated stall speed, progressively increase AOA until the stall

Brief the first unless your POH says otherwise, and know the published stall speed for 45° of bank, flaps up before you fly it — the AFM typically publishes it.

Slowly, then all at once. 60° of bank in a level turn is 2 Gs; 72° produces 3 Gs; 80° produces 5.76 Gs, and at slightly more than 80° the load factor exceeds 6 Gs — the limit load factor of an acrobatic airplane, which a normal-category trainer passed 30° of bank ago (PHAK ch. 5). The load factor increases at a terrific rate after about 45° to 50° of bank, and a 90°-banked level turn is not mathematically possible. For the average GA airplane, the practical maximum for a coordinated constant-altitude turn is about 60° — and an additional 10° of bank adds roughly 1 G (PHAK ch. 5).

Limit load factors vary by category:

A 50 percent safety factor is added to those limit loads, and for airplanes over 4,000 lb gross weight the normal-category limit is reduced. The category is placarded in the flight deck (PHAK ch. 5).

PHAK's own summary: an increased load factor increases the stresses on the aircraft structure, and an increased load factor increases the stalling speed and makes stalls possible at seemingly safe flight speeds (PHAK ch. 5). The second half is the accident — an airplane with a 50-knot 1G stall can be stalled at 100 knots by imposing 4 Gs. It also explains VA's own arithmetic: an older airplane stalling at 60 knots has VA near 102 knots (1.7 ×), and stalling it there imposes a load factor equal to the square of the speed increase — 2.89 G (PHAK ch. 5). Take the real VA from your POH.

Departure into a spin. The stall may arrive at an unexpected attitude, and failure to recover immediately may result in a spin or other departure from controlled flight (AFH ch. 5).

Mitigations, in order:

1. The 3,000 ft AGL floor (CA.VII.D.S2)
2. Rigorous coordination so the break is symmetric
3. Recovery at the first indication rather than exploring the full stall
4. AOA reduction before roll
5. A cleared area above and below

Also note why the standard requires the pull to be "smoothly and firmly" (CA.VII.D.S5): an abrupt pull spikes the load factor well above the 1.41 G the bank implies, sharpens the break, and appears on the AFH's error list as an inadvertent accelerated stall during a power-off or power-on stall entry (AFH ch. 5).

Turbulence: gusts add load factor you did not command, so the effective stall speed becomes a moving target and the margin above VA shrinks. PHAK's guidance is direct — in extremely rough air, as in thunderstorms or frontal conditions, it is wise to reduce the speed to the design maneuvering speed — and even then, gusts can produce loads that exceed the limits (PHAK ch. 5).

Density altitude: at high density altitude you have less power to arrest the descent in the recovery, so plan for greater altitude loss and hold more margin above the Task's 3,000 ft floor.

Limits: the 1G published stall speed the system is calibrated around is valid only in unaccelerated 1G flight, in coordinated flight, at one weight, and at one CG (AFH ch. 5). A 45° banked pull violates the first condition by design, so warning and buffet arrive at a higher indicated airspeed than the book number — certification permits that warning to be inherent pre-stall buffet rather than a device (AFH ch. 5).

In normal operations: the same thing shows up whenever you load the wing unintentionally — a steep turn, a firm pull-up for terrain or traffic, a gust. The response never changes: unload first, until the warning stops, then roll level coordinated and add power. Since this Task recovers at the first indication (CA.VII.D.S6), that cue is the whole margin.

It is the other way to reach the same accident, which is why CA.VII.D.R5 pairs secondary stalls, cross-control stalls, and spins. An overshooting base-to-final turn produces an accelerated stall when you pull — and a cross-control stall when you pull and feed in bottom rudder. Aileron one way with rudder the opposite way can stall with very little warning; the nose may pitch down, the bank angle may suddenly change, and the airplane may continue rolling toward inverted, which is usually the beginning of a spin (AFH ch. 5). The recovery is the same sequence: reduce AOA until the warning is eliminated, then roll wings level with ailerons coordinated with rudder before it becomes a spiral or spin. It is a demonstration-only maneuver — only flight instructor applicants perform it.

Reduce AOA until the stall warning is eliminated and hold it there before you do anything else, then roll level and add power. The classic secondary stall is an abrupt pull back to the original altitude — a natural impulse that is amplified as proximity to the ground increases (AFH ch. 5). Accept the altitude loss, fly out of it, and climb back at Vx or Vy.