Demonstration of Flight Characteristics at Various Configurations and Airspeeds (ASEL and ASES)

Task X.B is the teaching demonstration of the power-required curve. Slow flight (Task X.A) parks the airplane at one point near the stall and asks you to maneuver there. Task X.B walks the airplane down the whole curve — maneuvering speed, then best glide, then the critically slow speed — noting the power setting required at each step (AI.X.B.S4), and does it twice: clean, then landing configuration (AI.X.B.S4, S5).

The evaluator picks Task A or B, per the Area X note — so prepare both and expect one.

• Region of normal command — holding constant altitude, a higher airspeed requires a higher power setting and a lower airspeed requires a lower power setting. Most flying (climb, cruise, maneuvers) happens here (PHAK 11-11).
• 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 (PHAK 11-11).

The dividing line is the lowest point on the power-required curve — the speed for minimum power required, which is the best endurance airspeed (PHAK 11-11 and Figure 11-14). Everything between that speed and the stall speed is the region of reversed command.

No — and the PHAK says so in as many words: it "does not imply that a decrease in power produces lower airspeed" (PHAK 11-11). The relationship is between the power required to hold altitude and the airspeed you have chosen to hold altitude at. It is a statement about two stabilized, level-flight conditions, not about what happens in the three seconds after you move the throttle.

This is the single most-mistaught idea in the Task. Have a clean sentence ready.

Different optimizations, different points on different curves:

• L/D MAX is the minimum drag speed — the best lift-to-drag ratio, and therefore best glide (AFH 5-10).
• The minimum power required speed is the lowest point on the power-required curve — best endurance (PHAK 11-11).

Power is drag multiplied by velocity, so the minimum-power point sits at a slower speed than the minimum-drag point.

Now put them on the right side of the line, because this is where applicants get turned around: the minimum-power-required speed is the boundary — the regime between that speed and the stall speed is what PHAK calls the region of reversed command (PHAK 11-11). L/D MAX is faster than it, so L/D MAX sits in the region of normal command. That is exactly what AI.X.B.K3 asks you to explain: the minimum power required speed and its role in differentiating the region of normal command from the region of reversed command.

1. Design/operating maneuvering speed appropriate to today's weight — while describing the pitch, power, and trim inputs that hold altitude and airspeed (S4a).
2. Gear and flaps retracted, slow to and maintain best glide speed (or as specified), noting the power required (S4b).
3. Continue slowing to the airspeed where any further increase in AOA, increase in load factor, or reduction in power would result in an immediate stall; hold it in level flight, noting the airspeed and power required (S4c).
4. Verbally acknowledge the stall warning indications (S4d).
5. Without changing power, lower the pitch attitude and accelerate until level flight is reestablished — note the new airspeed and the altitude lost (S4e).
6. Return to normal cruise at the assigned altitude and heading (S4f).

That step is the lesson. At the same power setting there are two airspeeds that will hold level flight — one on each side of the minimum-power point. Lowering the nose without touching the throttle walks the airplane from the slow solution to the fast solution.

The altitude you lose getting there is the number the student needs to remember, because it is exactly what a low, slow, dragged-in final approach will cost them — and on short final that altitude may not exist. The PHAK's own example is the low-airspeed, high-pitch power approach for a short field: merely lowering the nose to regain flying speed "without the use of power, would result in a rapid sink rate and corresponding loss of altitude" (PHAK 11-11).

• Altitude: ±100 feet
• Airspeed: +5/−0 knots
• Heading: ±10°
• Bank: ±5°, as appropriate

(AI.X.B.S1). Looser on altitude than Task X.A's ±50 feet, because you are transiting speeds rather than parked at one.

Entry altitude must allow the maneuver to be completed no lower than 1,500 feet AGL (AI.X.B.S2), and you must clear the area (AI.X.B.S3).

You are also being graded on the talking: S1 says conduct and explain the procedure. Silence is a deficiency here in a way it isn't in most Tasks.

• Design/operating maneuvering speed (VA/VO) — not marked on the ASI; it varies with weight and lives in the POH. Do not use full or abrupt control movements at or above it (AC 61-67C, par. 100f).
• Landing gear extended/operating speed (VLE/VLO), if applicable — POH.
• Flaps extended/operating speed (VFE) — top of the white arc.
• Best glide speed — POH; the L/D MAX point.
• Reference landing speed — POH.
• Stalling speeds — VSO is the stall speed in the landing configuration and is the bottom of the white arc; VS1 is the stall speed in a specified configuration and is the bottom of the green arc (AC 61-67C, par. 100c–e).

The white-arc/green-arc comparison is the visual proof that flaps lower stall speed (AC 61-67C, par. 100c).

You walk the airplane down the whole speed range reading power and airspeed aloud, so teach what the two instruments can and cannot tell you.

Airspeed indicator:

• It shows indicated airspeed. The arcs are fixed marks set at one weight and one configuration — the white arc's lower limit is VSO and the green arc's lower limit is VS1 (AC 61-67C, par. 100c–e). Your actual stall speed moves with weight, CG, load factor, and contamination; the arc does not move with it.
• VA and VO are not marked at all — they change with weight and live only in the POH (AC 61-67C, par. 100f).
• Near the stall the numbers get least trustworthy: in uncoordinated flight the pitot/static instruments, especially the altimeter and airspeed indicator, are unreliable due to the uneven distribution of air pressure over the fuselage (AC 61-67C, par. 109).
• A listed common error is over-reliance on the airspeed indicator and slip-skid indicator while excluding other cues (AFH 5-21). AC 61-67C par. 200a(11) gives the antidote as an exercise: fly at low airspeeds with the ASI covered, at various flap settings, with distractions.

Stall warning indicator: it fires 4 to 8 knots prior to the onset of the stall (AC 61-67C, par. 103) — a narrow margin. It senses AOA at one point on one wing and knows nothing of load factor, bank, or contamination, and certification permits the warning to come from inherent aerodynamic qualities instead of a device, so some airplanes have none (AFH 5-13).

The teaching point: the ASI confirms what the airplane is telling you — it does not replace it.

VA is lower at lower weight. A lighter airplane accelerates more for a given gust or control deflection, so it reaches its design limit load factor at a lower speed. AC 61-67C states it plainly in the turbulence discussion: "Maneuvering speed is lower at a lower weight" (par. 100l).

The instructor-depth caveat students never hear: rapid and large alternating control inputs, especially combined with large changes in pitch, roll, or yaw, may result in structural failure at any speed, even below VA (AC 61-67C, par. 100f). VA is not a licence to slam the controls.

• Reciting instead of demonstrating — the student must hear the power setting as you read it, at each step. Say the number out loud.
• Changing power during step 5 (S4e/S5f) — the whole point is same power, new airspeed. Cover the throttle with a finger if you must.
• Exceeding VFE or VLE while configuring (AI.X.B.R2) — slow to the limiting airspeed first, then configure (S5b).
• Failing to verbally acknowledge the stall warning (S4d/S5e) — an explicit skill element; unacknowledged warnings are a listed risk (AI.X.B.R6).
• Letting the demonstration become slow flight — you are supposed to move through the regime, not live in it.
• Not connecting it to anything — close every run by naming the real-world scenario it models.

Draw power required on the vertical axis and airspeed on the horizontal. The curve is a U:

• Bottom of the U — the speed at which the lowest brake horsepower sustains level flight: the best endurance airspeed (PHAK 11-11).
• Right of the bottom — the region of normal command. Parasite drag dominates; faster costs more power.
• Left of the bottom — the region of reversed command. Induced drag dominates; slower costs more power.
• Overlay maximum power available as a second curve. The vertical gap between the two is excess power — your rate of climb (PHAK Figure 11-14).

Where the two curves meet on the left is where you have no excess power at all. That's the airplane's floor.

Both come straight from the PHAK (11-11):

1. The short-field power approach. Low airspeed, high pitch attitude. If an unacceptably high sink rate develops, power may stop the descent — but without further use of power the airplane would probably stall or be incapable of flaring.
2. The soft-field climbout. If the pilot tries to climb out of ground effect before attaining normal climb pitch attitude and airspeed, the airplane may inadvertently enter the region of reversed command at a dangerously low altitude. Even at full power it may be incapable of climbing or holding altitude. The only recourse is to lower the pitch attitude to increase airspeed — which inevitably results in a loss of altitude.

Teach both by name. They are the accident chain, not academic curiosities.

Teach it as regime-dependent, which is what the AFH actually says. Below L/D MAX, small pitch changes produce disproportionately large changes in induced drag and therefore airspeed, so pitch becomes the more effective control of airspeed and power the effective control of the flightpath (AFH 5-10).

Above L/D MAX the coupling loosens and the mantra is much weaker. If a student challenges it, the honest instructor answer is: "In cruise, pitch and power are both energy controls and neither one owns a variable. On approach, below L/D MAX, this rule is true enough to fly by — and that's where it matters."

Same architecture as clean, with configuration inserted:

1. Establish design/operating maneuvering speed for today's weight, describing pitch, power, and trim (S5a).
2. Slow to the limiting airspeeds and fully extend gear and flaps — VLO/VLE first, then inside the white arc for flaps (S5b).
3. With gear and flaps fully extended, slow to and maintain reference landing speed, noting the power required (S5c).
4. Continue to the critically slow airspeed in level flight, noting airspeed and power (S5d).
5. Verbally acknowledge the stall warning (S5e).
6. Without changing power, lower the nose and accelerate to level flight; note the new airspeed and altitude lost (S5f).
7. Return to cruise at the assigned altitude and heading (S5g).

The comparison between the two runs is the payoff — same airplane, same weight, wildly different power numbers.

Drag. In the landing configuration the airplane needs substantially more power to hold altitude at every airspeed, and the critically slow speed is lower because flaps generally increase the lifting ability of the wing and reduce stall speed (AC 61-67C, par. 100c).

Two instructional payoffs:

• The go-around. In landing configuration on a stabilized approach, at idle, the airplane is already left of the bottom of the power curve — slower than best endurance, deep in the region of reversed command, carrying the drag of full flaps and gear. That is the moment a go-around is initiated — which is exactly why the elevator trim stall (Task X.G) exists.
• Flap retraction discipline. Retract too fast at low speed and the AOA required jumps; AC 61-67C's list of go-around demonstrations includes retracting flaps rapidly while holding a high climb attitude, producing a secondary stall or settling with a loss of altitude (AC 61-67C, par. 200f).

• Altitude — plan the entry so the whole sequence finishes no lower than 1,500 feet AGL (AI.X.B.S2). The slow segments and the accelerate-back-to-level segment both cost altitude.
• Airspeed limits on the way down — this is the one Task in Area X where you are actively working near VA, VLE/VLO, and VFE. Overspeeding a flap while demonstrating is an unsatisfactory outcome and a listed risk (AI.X.B.R2).
• Critically slow airspeed (AI.X.B.R9) — the student's hands are on the controls at the exact speed where control response is worst. Keep your hands near, brief the exchange, and take the controls at the first sign of uncommanded yaw.
• Environment — turbulence can produce an abrupt increase in AOA and stall the airplane well above the book speed (AC 61-67C, par. 100l). In rough air, add margin or postpone.
• Collision (AI.X.B.R8) — clearing turns before entry, and eyes outside during the slow segments where the nose is high and blocking the view.