Aerodynamics and Spin Awareness

Four forces act on an airplane in flight: lift, weight, thrust, and drag. In steady, unaccelerated flight the opposing pairs are equal. The handbook says the airplane "continues to move and gain speed until thrust and drag are equal," and that "lift and weight must be equal to maintain a constant altitude" 1. A climb, a descent, or a change of speed is a change in one of those pairs.

Angle of attack

The angle of attack is "the acute angle between the chord line of the airfoil and the direction of the relative wind" 2. The chord line runs from the leading edge of the wing to the trailing edge. The relative wind is the air coming at the wing, opposite the direction the wing is moving. The angle of attack is not the angle between the nose and the horizon. A wing in a steep dive can be at a high angle of attack if the pilot pulls hard. A wing in a climb can be at a low angle of attack if the airplane is fast.

How the wing makes lift

The wing deflects air downward and creates a pressure difference between its upper and lower surfaces. Both effects produce lift. The pilot controls lift with the angle of attack. The handbook says that "any time the control yoke or stick is moved fore or aft, the AOA is changed," and that "as the AOA increases, lift increases (all other factors being equal)" 3. Lift also rises with airspeed. At a given angle of attack, more airspeed means more lift.

The rise in lift with angle of attack has a limit. "When the aircraft reaches the maximum AOA, lift begins to diminish rapidly. This is the stalling AOA, known as CL-MAX critical AOA." Figure 5-5 in the handbook shows the lift curve rising to the critical angle and falling after it. For a typical wing the critical angle is about 18 to 20 degrees. The number does not change with airspeed, weight, or attitude.

One cause

A wing stalls when it exceeds its critical angle of attack. Nothing else stalls a wing. The advisory circular on stall and spin awareness says a stall "occurs when an aircraft is flown at an angle of attack (AOA) greater than the angle for maximum lift" 4. The wing can reach that angle at any airspeed, in any attitude, and at any weight.

A slow airplane in level flight stalls when the pilot raises the nose past the critical angle. A fast airplane in a steep turn stalls when the pilot pulls past the same angle. The airspeed indicator shows different numbers. The angle of attack is the same.

The published stall speed is a number for one condition. The Airplane Flying Handbook says the level-flight 1G stall speed is valid only under four conditions 5:

• unaccelerated 1G flight
• coordinated flight
• one weight
• one center of gravity.

A change in any of the four changes the airspeed at which the wing reaches the critical angle.

Sight, sound, and feel

A pilot detects an impending stall through three senses 5:

• sight: a nose attitude higher than the attitude for the airspeed
• sound: the slipstream quiets as the airspeed falls, and the stall horn sounds
• feel: soft, less effective controls, a late response to control movement, and a buffet in the controls just before the stall.

The handbook says a pilot "will feel control pressures change as speed is reduced" and needs "larger control movements to get the desired airplane response." Kinesthesia, the sense of changing direction or speed, warns a trained pilot before the horn sounds.

The horn's margin

A stall warning device sounds before the stall. The advisory circular says most devices "alert the pilot 4 to 8 knots prior to the onset of a stall" 6. The Warrior's horn "sounds automatically at between 5 and 10 miles per hour above stall speed" 7.

That margin is a margin of airspeed in slow, level, coordinated flight. An abrupt pull shortens it, because the angle of attack rises faster than the airspeed falls. Load factor shortens it, because the stall speed rises with the load. A pilot who pulls hard in a steep turn can hear the horn and stall in the same second. The horn sounds at a fixed margin. The time between the horn and the stall depends on how fast the pilot pulls.

The flight of N444PM

On June 28, 2022, a 64-year-old private pilot took off alone from Pearson Field in Vancouver, Washington, in his Beech Bonanza. Three minutes later he decided to return because of low clouds. Seventeen minutes after takeoff he turned from base to final over the runway threshold. He banked past 60 degrees to line up with the runway. The wing stalled. The airplane struck the ground on its right wing and burned, and he died 8.

He held a private pilot certificate with about 600 hours and no instrument rating. His third-class medical was five months old. The Bonanza was a 1976 V35B with a 285-horsepower engine, and a friend helped him buy it. That friend was a flight instructor. He flew at least 30 hours with the pilot in the airplane and gave him his most recent flight review. He taught him normal and accelerated stalls in it.

He took off at 7:23 in the morning and flew east, talking to Portland tower. At 7:26 he told the controller he was going to "circle back" because of clouds. He said he would fly to Vancouver Lake, lose some altitude, and "see if this clears." For the next two or three minutes he and the controller worked on a transponder problem while he flew northwest.

At 7:30 he told the controller he was "wondering about the weather," that he "thought it was 4,000 ft, but it's a lot lower than that." The controller offered to send him to approach control for weather. At 7:34 the controller learned he never checked in with approach. He was over Vancouver Lake, four miles from the field, and said he would return to Pearson.

At 7:35 he announced on the common frequency that he was entering the downwind. A minute later he announced he was on downwind. That transmission was his last. Abeam the runway threshold he turned base, early. His friend told investigators they normally turned final over a large white building about half a mile from the runway. The investigators could not determine why he turned where he did.

The ADS-B data showed a stabilized base leg:

• about 80 knots calibrated airspeed
• a descent of about 1,000 feet per minute
• about 7 degrees of bank
• an angle of attack of about 5 degrees.

Just past the runway threshold, the airplane turned right about 90 degrees toward the runway. Surveillance video showed a slight right bank steepening within two seconds into a rapid descent. The right wing struck the ground first, near vertical, and the airplane slid inverted along the displaced threshold of runway 26.

The bank angle in that last turn exceeded 60 degrees. The investigators used the airplane's stall chart. At that bank the stall speed was more than 80 knots. The ADS-B data put the airspeed at about 73 knots. The airplane weighed about 2,562 pounds against a maximum of 3,412. The engine showed no defect. The weather at the field was not a factor.

The NTSB's probable cause is "the pilot's decision to execute a steep turn to final approach, which resulted in an exceedance of the airplane's critical angle of attack and an accelerated stall." The contributing factor was "the improper positioning on base leg and the pilot's subsequent decision to continue the approach."

Where the accident chain could have been broken

The accident was five decisions. Each is listed below with its PAVE category and the decision that would have ended the flight safely at that point. The pilot made the last two inside one minute, and the last one inside two seconds.

Load factor

Load factor is lift divided by weight, measured in Gs. In level flight the wing lifts the airplane's weight and the load factor is 1. In a level turn the wing must lift the weight and also pull the airplane around the turn. It makes more lift than the weight. The handbook says "the load factor for any aircraft in a coordinated level turn at 60° bank is 2 Gs" 9.

At 45 degrees the load factor is 1.41. At 80 degrees it is 5.76. The number depends on the bank angle only. A Warrior, a Bonanza, and an airliner at 60 degrees of bank in a level turn all carry 2 Gs.

The load factor "increases at a terrific rate after a bank has reached 45° or 50°." The Airplane Flying Handbook says the same thing about steep turns: "with a load factor of 2.0, the effective weight of the aircraft (and its occupants) doubles" 10.

The stall speed rises with the square root

More lift at the same airspeed means a higher angle of attack. The airplane reaches the critical angle at a higher airspeed under load. The handbook says "an aircraft's stalling speed increases in proportion to the square root of the load factor" 11. At 2 Gs the stall speed is 1.41 times the wings-level number, because the square root of 2 is 1.414. At 4 Gs it doubles. The handbook's example is an airplane that stalls at 50 knots wings level and "can be stalled at 100 knots by inducing a load factor of 4 Gs."

The Warrior's chart

The Warrior's flight manual shows the same arithmetic on page 3-7 12. Power off, at gross weight, flaps up, the stall speed is 64.5 mph wings level and 91 mph at 60 degrees of bank. Flaps down it is 58 and 82. Ninety-one divided by 64.5 is 1.41. The table in between gives 67 at 20 degrees, 74 at 40, and 80 at 50. The Bonanza at Pearson Field stalled at more than 80 knots for the same reason, in a turn past 60 degrees.

Weight and center of gravity

Weight raises the stall speed. A heavier airplane needs more lift at each airspeed, so it reaches the critical angle sooner. The Warrior's manual says "stall speeds at lower weights will be correspondingly less" 7.

The center of gravity also changes the stall speed. The tail pushes down to hold the nose up, and the wing lifts the weight plus that push. With the center of gravity forward the tail pushes harder, and the stall speed rises a little. With the center of gravity aft the tail pushes less and the stall speed falls, and the airplane becomes less stable.

An aft center of gravity also makes spin recovery harder. The handbook says an airplane "that cleanly recovers from a prolonged spin with the CG at one position may fail completely to respond to normal recovery attempts when the CG is moved aft by one or two inches" 13. The advisory circular compares the two categories. An airplane loaded in the normal category, with more weight and a further aft limit, "could have less resistance to spin entry" than the same airplane loaded for utility 4.

Two kinds of drag

Drag has two parts. Parasite drag is "all the forces that work to slow an aircraft's movement" that are not associated with making lift 14. Its sources are the shape of the airplane, the friction of air on its skin, and the interference where parts meet. It grows with the square of the airspeed. Twice the speed makes four times the parasite drag.

Induced drag is the part of drag that comes from making lift. The handbook says it "is inherent whenever an airfoil is producing lift" and "it is always present if lift is produced." It grows as the airspeed falls, because the wing needs a higher angle of attack to hold the airplane up. Total drag is the sum of the two. The total is lowest at the airspeed where the two curves cross, and the handbook calls that point L/DMAX, "the most lift for the least amount of drag."

The region of reversed command

Above the speed for minimum power, flying faster takes more power. Below it, flying slower takes more power too, because induced drag rises faster than parasite drag falls. The handbook calls that regime the region of reversed command: "flight in which a higher airspeed requires a lower power setting and a lower airspeed requires a higher power setting to hold altitude" 15. The boundary is the speed for maximum endurance, the lowest point on the power-required curve. That speed is a little below best glide speed.

A pilot in the region of reversed command who raises the nose to stop a descent makes the descent worse. The airplane slows, the drag rises, and the descent rate grows. Power stops the descent. Lowering the nose stops the descent. Pulling does not.

Slow flight

Slow flight is flight near the stall, with the airplane still under control. The Airplane Flying Handbook sets the target at "5 to 10 knots above the 1G stall speed" 16. In slow flight "any further increase in angle of attack, increase in load factor, or reduction in power, will result in a stall warning."

The controls feel soft. The nose sits high. The airplane needs more right rudder, because the propeller effects grow at high power and low speed. The airplane is in the region of reversed command, so holding altitude at a lower speed takes more power, not less. Flaps and gear change the speeds but not the relationship.

The emergency that is already happening

Unintended slow flight on an approach, with the stall horn on, is an emergency. A pilot in it does not need to wait for the stall. The handbook says pilots "should react to and correct for any stall indication" 16. The correction is the first two steps of the stall recovery: lower the nose to reduce the angle of attack, and add power 17. The pilot does both at once, before any other task, including the radio and the flaps.

The ball

Coordinated flight is flight with no sideslip. The ball in the inclinometer sits in the center. A ball out of the center means the airplane is slipping or skidding. In a skid the ball is on the outside of the turn, and the airplane is yawing into the turn faster than it is banking. In a slip the ball is on the inside. The rule is "step on the ball": press the rudder on the side the ball has moved to.

The Airplane Flying Handbook links uncoordinated flight to the spin. "Situations can develop when a pilot maintains certain uncoordinated flight control deflections, which create the potential for a spin. This is especially hazardous when operating at low altitudes, such as when operating in the airport traffic pattern" 18. A stall in coordinated flight drops the nose. A stall in uncoordinated flight drops a wing, and the yaw that was already there turns the stall into a spin.

Four left-turning tendencies

A single-engine airplane with a propeller that turns clockwise from the pilot's seat yaws and rolls left. The handbook names four causes 19:

• torque reaction: the engine turns the propeller one way and the airplane rolls the other way
• the corkscrewing slipstream: the propeller wash spirals back and strikes the left side of the vertical fin, yawing the nose left
• gyroscopic precession: a force on the propeller disc acts 90 degrees later in its rotation, so raising the tail yaws the nose left
• P-factor: the descending blade on the right makes more thrust than the ascending blade on the left, and the nose yaws left.

Right rudder corrects all four.

P-factor

P-factor is strongest at high power and high angle of attack. The handbook says that "when an aircraft is flying with a high AOA, the 'bite' of the downward moving blade is greater than the 'bite' of the upward moving blade," which "moves the center of thrust to the right of the prop disc area, causing a yawing moment toward the left" 19. Takeoff, the climb after it, and a go-around are flown at high power and high angle of attack. A departure stall is a stall with yaw already present. The yaw is the left yaw the right rudder opposes.

Adverse yaw

Adverse yaw is the nose yawing away from the turn as the turn begins. The aileron that goes down on the rising wing adds lift and adds drag, and the drag pulls that wing back. The handbook says "the yaw is opposite the direction of the bank" and "adverse yaw becomes more pronounced at low airspeeds" 20. Rudder in the direction of the turn, applied with the aileron, cancels it. The Airplane Flying Handbook says the rudder "does not turn the airplane" and "is used to maintain coordinated flight" 18.

Overbanking

In a steep turn the outside wing travels a longer path than the inside wing in the same time. It moves faster and makes more lift. The handbook describes the result: "the wing on the outside of the turning moment travels forward faster than the inside wing and, as a consequence, its lift becomes greater. This produces an overbanking tendency which, if not corrected by the pilot, results in the bank angle becoming steeper and steeper" 21. The pilot corrects it with aileron against the turn. The Airplane Flying Handbook lists "the airplane's inherent overbanking tendency" second among five effects of a steep turn 10.

Rate and radius

Bank angle and airspeed set the turn. The handbook says that "if the airspeed is held constant, an aircraft's ROT increases if the bank angle is increased," and that at a constant bank angle more airspeed makes a wider radius 22. A steeper bank makes a faster, tighter turn. More speed at the same bank makes a slower, wider turn. Over the ground, the groundspeed sets the radius. A tailwind on base widens the turn to final and carries the airplane through the extended centerline.

Ground effect

Within about one wingspan of the surface, the ground interferes with the airflow around the wing. The handbook says the surface restricts the vertical component of the airflow, which "alters the wing's upwash, downwash, and wingtip vortices" 23. Smaller vortices mean less induced drag at the same angle of attack. On takeoff the airplane can lift off in ground effect at a speed at which it cannot climb out of it. On landing the airplane floats in the flare, because the drag that was slowing it is reduced. A pilot who pulls a Warrior off early can climb to a wingspan of height and stop climbing.

The recovery, in order

The Airplane Flying Handbook gives a stall recovery in six steps and says "the most important action to an impending stall or a full stall is to reduce the AOA" 17. For a Warrior the steps are four:

1. Pitch nose-down to reduce the angle of attack
2. Roll wings level with coordinated aileron and rudder
3. Add power as needed
4. Return to the desired flight path.

The handbook's first step is "Push forward on the flight controls to reduce the AOA below the critical AOA until the impending stall indications are eliminated before proceeding to the next step." Its second step adds: "It is important not to be tempted to control the bank angle prior to reducing AOA." For power it says "Advance the throttle promptly, but smoothly."

The order matters. The handbook says there "have been numerous situations where pilots did not first reduce AOA, and instead prioritized power and maintaining altitude, which resulted in a loss of control."

Where power-off stalls happen

A student practices the power-off stall at altitude in the landing configuration. An unintended power-off stall happens on the approach. The handbook names the places: the turn from base to final with the controls misused, "trying to stretch a glide after the engine has failed," and being "low on the approach to landing" 24. The advisory circular adds "attempting to recover from a high sink rate on final approach by using only an increased pitch attitude" and "improper airspeed control on final approach" 25. Distraction in the pattern is common to all of them.

The base-to-final cross-control stall

The base-to-final spin entry follows one sequence. The pilot overshoots the turn to final, often because a tailwind on base pushed the airplane through the centerline. The handbook describes what comes next: "the pilot attempts to correct by increasing the bank angle, increasing back elevator pressure, and applying excess rudder in the direction of the turn (i.e., inside or bottom rudder pressure) to bring the nose around further to align it with the runway" 26.

The skid steepens the bank. The nose drops. The pilot pulls. The airplane is slow, skidding, cross-controlled, and at the critical angle. The inside wing stalls first. "Should a stall be encountered with these inputs, the airplane may rapidly enter a spin."

At pattern altitude there is not enough altitude to recover. "The safest action for an 'overshoot' is to perform a go-around." The handbook adds that on the turn to final a pilot "should be reluctant to use bank angles greater than 30 degrees." The Bonanza at Pearson Field stalled in a steep turn, not a skid. The go-around was the correct action in both cases.

The secondary stall

A secondary stall is a second stall caused by recovering from the first one too fast. The handbook says the pilot's "natural impulse is to bring the nose up as soon as possible and to do so abruptly," and that "this reaction is amplified as proximity to the ground increases" 27. The recovery is the same recovery: relax the pull, reduce the angle of attack, and recover again.

The accelerated stall

An accelerated stall is a stall above the normal stall speed, caused by load factor. The handbook says an airplane "can also stall at a higher indicated airspeed when the airplane is subject to an acceleration greater than +1G, such as when turning, pulling up, or other abrupt changes in flightpath" 28. It "would most frequently occur inadvertently during improperly executed turns, stall and spin recoveries, pullouts from steep dives, or when overshooting a base to final turn." The NTSB quoted that paragraph in the report on N444PM. The stall comes with little warning because the horn's margin is an airspeed margin, and the airspeed is above it.

The elevator trim stall

An airplane trimmed for a landing approach at idle power has nose-up trim. Full power for a go-around, with that trim, pitches the nose up hard. The handbook describes the elevator trim stall as "what can happen when the pilot applies full power for a go-around without maintaining positive control of the airplane" 29. It can happen on "a go-around procedure from a normal landing approach or a simulated, forced-landing approach, or immediately after a takeoff." The recovery is heavy forward pressure against the trim as the power comes in, then trim, then climb. A pilot who has not felt that pressure at altitude feels it first at 200 feet.

Power-on stalls

A power-on stall, the departure stall, happens at high power and low speed. Pilots practice it "to help the pilot recognize the potential for an accidental stall during takeoff, go around, climb, or when trying to clear an obstacle" 30. The advisory circular says "many stall/spin accidents have occurred during these phases of flight, particularly during go-arounds," and names the causes: "a nose-high trim setting or premature flap retraction" 25. At high power and high angle of attack the left-turning tendencies are strongest. The stall begins with yaw already present, and a departure stall with the ball out of the center is a spin entry.

What a spin is

A spin is an aggravated stall with autorotation. The handbook says "a spin occurs when at least one of the airplane's wings exceed the critical AOA (stall) with a sideslip or yaw acting on the airplane at, or beyond, the actual stall" 31. One wing is more deeply stalled than the other. It makes less lift and more drag, the airplane rolls and yaws toward it, and the rotation continues without further input. The advisory circular states the rule: "If a stall does not occur, a spin cannot occur" 4.

The yaw has a source. The handbook lists the sources: "incorrect rudder application," adverse yaw from the ailerons, "p-factor, torque, spiraling slipstream, and gyroscopic precession," and wind shear. The pilot supplied most of them. A stall with the ball centered and the rudder holding the nose straight does not spin.

Three phases

A spin has three phases 32:

• entry: the stall, plus the yaw
• incipient: "from the time the airplane stalls and starts rotating until the spin has fully developed," which "may take two to four turns for most airplanes"
• developed: rotation rate, airspeed, and vertical speed "are stabilized in a flightpath that is nearly vertical."

Recovery is quickest in the incipient phase. The handbook says a pilot "should initiate incipient spin recovery procedures prior to completing 360° of rotation."

PARE

The generic recovery is PARE, the first four of the handbook's six steps 33:

• Power to idle. "Power aggravates spin characteristics."
• Ailerons neutral. Aileron either way can delay the recovery or flatten the spin.
• Rudder full opposite the rotation, "brisk and full."
• Elevator briskly forward, "immediately after full rudder application. Do not wait for the rotation to stop before performing this step."

Step five is to "neutralize the rudder after spin rotation stops." Step six is to "apply back elevator pressure to return to level flight," with care, because "excessive back elevator pressure can cause a secondary stall and may result in another spin."

The Warrior's six steps

The Warrior's flight manual gives its own recovery, and the manual's procedure takes precedence over the generic one. Page 3-5 lists six steps 34:

• throttle, idle
• ailerons, neutral
• rudder, full opposite to direction of rotation
• control wheel, full forward
• rudder, neutral when rotation stops
• control wheel, as required to smoothly regain level flight attitude.

A pilot who learned PARE can forget the last two steps. A pilot who stops at "control wheel full forward" with full rudder still applied is in a dive with yaw. The pull-out from that dive is a split-S.

Spins are prohibited

The same page begins, "Intentional spins are prohibited." The placard on the panel says "SPINS ARE PROHIBITED FOR NORMAL AND UTILITY CATEGORIES" 35. Prohibited is not the same as impossible. The Warrior spins if it is stalled and yawed, and a pilot memorizes the recovery for that reason.

The utility category

The Warrior is certificated in two categories. The normal category allows 2,325 pounds and a load factor of 3.8. The utility category allows 1,950 pounds and a load factor of 4.4 36. The placard on the baggage door says "UTILITY CATEGORY OPERATION - NO BAGGAGE OR AFT PASSENGERS ALLOWED" 35. Utility category exists for three training maneuvers: steep turns, lazy eights, and chandelles, each entered at 124 mph. It does not exist for spins. Spins are prohibited in both categories.

Maneuvering speed

Maneuvering speed, VA, is "the speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane" 37. Below VA the wing stalls before the load reaches the structural limit. Above VA the structure can reach its limit before the wing stalls. The Warrior's VA is 124 mph, and the placard on the panel reads "ROUGH AIR OR MANEUVERING SPEED - 124 MPH" 35. The manual says to slow to maneuvering speed when turbulent air "is encountered or expected" 38.

VA falls with weight

The placarded VA is for gross weight. A lighter airplane stalls at a lower speed, so it can reach the limit load factor at a lower airspeed. The handbook relates VA to the stall speed: about 1.7 times the normal stall speed for older designs 37. The Warrior's manual says stall speeds at lower weights "will be correspondingly less" 7. A Warrior with one pilot and half tanks has a VA below 124 mph. A pilot who wants the protection at light weight slows further.

One input, one axis

VA protects against one full input on one axis. The handbook says the protection does not cover "multiple full control inputs in one axis or full control inputs in more than one axis at the same time" 37. Full alternating rudder, or full aileron with full elevator together, can break the airplane below VA. The number is a limit for a single control, moved once.

The limit speeds

The Warrior's airspeed limitations are in calibrated miles per hour, on page 3-2 of the flight manual 36:

• VNE, never exceed: 176 mph, the red line
• VNO, maximum structural cruising: 140 mph, the top of the green arc, and the yellow arc above it is for smooth air only
• VA, maneuvering: 124 mph
• VS1, stall with flaps up: 64.5 mph, the bottom of the green arc
• VSO, stall in the landing configuration: 58 mph, the bottom of the white arc.

The flap speed by serial number

The flap limit speed, VFE, depends on the airplane. The manual gives 125 mph "on serial nos. 7415001 through 7515449" and 115 mph "on serial nos. 7615001 and up" 36. The white arc is marked to match. A pilot who flies two different Warriors checks the serial number and the arc before extending flaps at 120.

Climb speeds

The best rate of climb speed, VY, is 87 mph. The manual's climb page gives it and adds a best angle of climb at 76 mph, flaps up 7. The short-field takeoff procedure uses a different speed with 25 degrees of flap: "Accelerate to 66 MPH CAS and rotate, maintaining 66 MPH CAS until obstacle clearance has been attained. After the obstacle has been cleared accelerate to 87 miles per hour and then slowly retract the flaps" 39. The pilot holds 66 mph until the obstacle is cleared and 87 mph after it.

Density altitude

Density altitude is "pressure altitude corrected for nonstandard temperature" 40. Hot, high, and humid air is thin air. Thin air reduces three things at once:

• engine power, because the engine takes in less air
• propeller thrust, because the propeller has less air to push
• lift, because the wing has less air to deflect.

The same indicated airspeed means the same angle of attack, so the airplane rotates and stalls at the same indicated speeds. It reaches those speeds later on the runway and climbs more slowly after them.

Gusts and shear

The relative wind is the air the wing meets. A gust or a wind shear changes that air without any input from the pilot, and so changes the angle of attack. The handbook says wind shear "can rapidly change the performance of the aircraft and disrupt the normal flight attitude" 41. An updraft raises the angle of attack. A headwind that drops to a tailwind lowers the airspeed. The margin above the stall must grow when the air is rough, and the manual's speed for turbulence is maneuvering speed 38.

The practice rules

Pilots practice stalls at altitude. The ACS requires an entry altitude that allows each stall task "to be completed no lower than 1,500 feet above ground level (AGL)" in a single-engine airplane 42. The Airplane Flying Handbook gives the same floor and adds "or higher if recommended by the AFM/POH" 24. The Warrior's manual reports 100 to 275 feet of altitude lost in its certification stalls 12.

The first skill element of each stall task is "clear the area" 42. Clearing turns come before the maneuver, and collision vigilance continues through it. With the nose high, the pilot cannot see the airspace ahead.

Distraction

Most stall and spin accidents begin with a distraction. The advisory circular cites NTSB statistics that "most stall/spin accidents result when a pilot is distracted momentarily from the primary task of flying the aircraft" 43. Its list of distractions is ordinary: "locating a checklist," "flying a traffic pattern on a windy day," "reading a chart or making fuel and/or distance calculations," "attempting to retrieve items from the floor, back seat, or glove compartment." The pilot of N444PM spent eight minutes on a transponder. The defense is deliberate division of attention: fly the airplane first, then handle the task, and postpone the task when the flying requires it.