Performance and Limitations (ACS Task F)

Performance numbers come from the manual's charts. The pilot enters each chart with the weight, wind, temperature, and altitude of the flight. The pilot enters the Warrior's takeoff chart at the density altitude and reads across to the distance for the flap setting 1. A number from memory was computed for another flight's conditions. The Pilot's Handbook: "By using these performance charts, a pilot can determine the runway length needed to take off and land, the amount of fuel to be used during flight, and the time required to arrive at the destination" 2.

Interpolate, and round the adverse way

When the conditions fall between the rows, the pilot interpolates. The handbook: "Interpolating information means that by taking the known information, a pilot can compute intermediate information. However, pilots sometimes round off values from charts to a more conservative figure. Using values that reflect slightly more adverse conditions provides a reasonable estimate of performance information and gives a slight margin of safety" 3. When an input is uncertain, the pilot rounds it in the direction that makes the answer worse:

• the temperature up
• the weight up
• the headwind down.

The chart's conditions are part of the number

A chart's title block is part of the data. The Warrior's takeoff chart reads "PAVED LEVEL DRY RUNWAY. GROSS WEIGHT 2325 LBS. NO WIND. FULL POWER BEFORE BRAKE RELEASE. EXTRAPOLATION OF CHART ABOVE 7000 FT. IS INVALID," and names the flap setting and the rotation speed for each line 1. The landing chart reads "POWER OFF. 40° FLAPS. PAVED LEVEL DRY RUNWAY. NO WIND. MAX. BRAKING. APPROACH SPEED 73 MPH CAS" 4. Each of these conditions voids the number read from the chart:

• a grass runway
• a tailwind
• 20 degrees of flap
• 80 mph on the approach.

Book performance is a test pilot's number

A test pilot in a new airplane produced the book's numbers. The handbook: "Information the manufacturer provides on these charts has been gathered from test flights conducted in a new aircraft, under normal operating conditions while using average piloting skills, and with the aircraft and engine in good working order" 2. Piper's own note above the Warrior's figures: "Performance for a specific airplane may vary from published figures depending upon the equipment installed, the condition of engine, airplane and equipment, atmospheric conditions and piloting technique" 5. A 50-year-old trainer flown by a private pilot does not match the book 6. The pilot adds the margin. The pilot does not hope for it.

The 50 percent margin

North Aero's standing safety factor on computed takeoff and landing distance is 50 percent. A chart distance of 1,600 feet over the obstacle is a planning distance of 2,400 feet. The factor converts book numbers into planning numbers. The pilot compares the runway with the planning number. The Airplane Flying Handbook makes the check part of preflight planning: "the pilot should check the POH/AFM performance charts to determine the predicted performance and decide if the airplane is capable of a safe takeoff and climb for the conditions and location" 7.

The abort point

The pilot chooses an abort point before takeoff. The Airplane Flying Handbook: "Prior to takeoff, the pilot should identify a point along the runway at which the airplane should be airborne. If that point is reached and the airplane is not airborne, immediate action should be taken to discontinue the takeoff" 8. The point is a spot the pilot can see from the cockpit: a taxiway, a windsock, a runway marking. If the airplane is not flying at that point, or is not accelerating as planned before it, the pilot stops the takeoff. The handbook's sizing rule: "The POH/AFM ground roll distances for take-off and landing added together provide a good estimate of the total runway needed to accelerate and then stop" 8.

Pressure altitude is the altimeter reading with 29.92 set. The handbook: "If the altimeter is set for 29.92 "Hg SDP, the altitude indicated is the pressure altitude—the altitude in the standard atmosphere corresponding to the sensed pressure" 9. Pressure altitude is the entry point for most performance charts. The handbook gives three ways to find it 9:

• set 29.92 and read the altimeter
• correct the indicated altitude for the altimeter setting
• use the flight computer.

Density altitude

Density altitude is pressure altitude corrected for nonstandard temperature. The handbook: "Regardless of the actual altitude at which the aircraft is operating, it will perform as though it were operating at an altitude equal to the existing density altitude" 10. The airplane performs as if it were at the density altitude. The handbook's example: a pressure altitude of 5,000 feet with a temperature 20 degrees above standard gives a density altitude above 7,000 feet. There a 790-foot ground run becomes "closer to 1,000 feet" 10.

The standard atmosphere

Each chart uses the standard atmosphere as its reference. The handbook: "The standard atmosphere at sea level has a surface temperature of 59 degrees Fahrenheit (°F) or 15 degrees Celsius (°C) and a surface pressure of 29.92 inches of mercury ("Hg) or 1013.2 millibars (mb)" 11. The standard temperature falls about 2 degrees Celsius per thousand feet, so the standard temperature at a 5,000-foot field is 5 degrees Celsius. A 30-degree day there is 25 degrees above standard.

Hot, high, or humid

Each of the three conditions raises density altitude by itself. The handbook: "The conditions that result in a high density altitude are high elevations, low atmospheric pressures, high temperatures, high humidity, or some combination of these factors" 10. One of the three is enough. The FAA's pamphlet: "Hot, high, and humid weather conditions can cause a routine takeoff or landing to become an accident in less time than it takes to tell about it," and "if an airport whose elevation is 500 MSL has a reported density altitude of 5,000 feet, aircraft operating to and from that airport will perform as if the airport elevation were 5,000 feet" 12. A hot day at a low-elevation field can be the accident, in the pamphlet's words.

Three losses at once

High density altitude reduces performance three ways. The wing makes less lift in thin air. The propeller makes less thrust. The engine makes less power. The pamphlet: "reduced air density (reported in terms of density altitude) adversely affects aerodynamic performance and decreases the engine's horsepower output. Takeoff distance, power available (in normally aspirated engines), and climb rate are all adversely affected" 12.

The three losses add together. The Koch chart's example: at 100 degrees Fahrenheit and 6,000 feet of pressure altitude, "230 percent must be added" to the takeoff distance, and a 500-foot-per-minute climb "would become 120 feet per minute" 13.

The working rule

Density altitude rises about 120 feet for each degree Celsius above standard, as a working rule. The pamphlet's rule-of-thumb chart runs a little under the rule and gives three points for a sea level field 14:

• 80 degrees Fahrenheit is a density altitude of 1,200 feet
• 100 degrees is 2,500 feet
• 120 degrees is 3,800 feet.

The pilot uses the rule to decide whether to open the chart. The flight computer or the handbook's chart gives the number for the log 10.

Humidity is the smallest of the three

Humidity has a real effect, and it is the smallest of the three conditions. The handbook: "Water vapor is lighter than air; consequently, moist air is lighter than dry air," and "Humidity alone is usually not considered an essential factor in calculating density altitude and aircraft performance; however, it does contribute" 15. Saturated warm air is only about one percent less dense than dry air at the same temperature and pressure. The pamphlet: "Humidity is not generally considered a major factor in density altitude computations because the effect of humidity is related to engine power rather than aerodynamic efficiency," and when the air is humid "it is wise to add 10 percent to your computed takeoff distance and anticipate a reduced climb rate" 16. Temperature and altitude dominate. Humidity is the extra ten percent on the takeoff distance.

A high density altitude does not by itself cancel a flight. It is a number the pilot plans the runway, the weight, and the climb around. The pamphlet: "it is advisable, when performance is in question, to schedule operations during the cool hours of the day (early morning or late afternoon)" 16. The options are:

• less weight, by fuel or by people
• a cooler hour
• a longer runway
• a route that needs less climb
• no flight, when the computed distance does not fit the runway.

The automated weather station broadcasts the number. The Aviation Weather Handbook: density altitude is "Included in the ASOS and AWOS broadcasts (phone and radio) when density altitude exceeds the field elevation by more than 1,000 ft. A density altitude advisory (i.e., 'check density altitude') is broadcast on ATIS when appropriate" 17. Above 5,000 feet of density altitude the pamphlet also directs the pilot to lean the engine for takeoff: "it is also essential to lean normally aspirated engines for maximum power on takeoff" 18.

Landing is a density altitude problem too

The same indicated approach speed is a higher true airspeed and a higher groundspeed at a high density altitude. The airplane covers the runway faster and the rollout is longer. The pamphlet's list of effects ends with "Increased TAS (but same IAS) on approach and landing" and "Increased landing roll distance" 12. The Warrior's landing distances rise with density altitude for that reason, and the pilot flies the same 73 mph on the dial 4.

Density altitude applies to the go-around

An airplane in a go-around at a high density altitude field may barely climb. The Koch chart's 500 feet per minute that became 120 applies to the go-around too 13. The pilot decides the runway before taxi, and the go-around path and the obstacles under it are part of that decision. A pilot who would not take off from a runway does not plan an approach whose go-around needs the same climb.

A headwind shortens takeoff and landing distance. A tailwind lengthens it, and lengthens it more per knot. The handbook: "A headwind that is 10 percent of the takeoff airspeed reduces the takeoff distance approximately 19 percent. However, a tailwind that is 10 percent of the takeoff airspeed increases the takeoff distance approximately 21 percent" 19. "The effect of wind on landing distance is identical to its effect on takeoff distance" 19. The Warrior's charts assume no wind. The pilot adds the tailwind penalty and keeps the headwind credit as margin.

Only the components count

The pilot splits the reported wind into a headwind component and a crosswind component. The handbook: "The crosswind and headwind component chart allows for figuring the headwind and crosswind component for any given wind direction and velocity" 20. A wind of 20 knots at 60 degrees to the runway is 10 knots of headwind and 17 of crosswind. The pilot enters the 10 knots in the distance chart and compares the 17 knots with the demonstrated crosswind.

Demonstrated, not limiting

The maximum demonstrated crosswind is a demonstrated value, not a limitation. The handbook: "The aircraft is tested by a pilot with average piloting skills in 90° crosswinds with a velocity up to 0.2 VS0 or two-tenths of the aircraft's stalling speed with power off, gear down, and flaps down. This means that if the stalling speed of the aircraft is 45 knots, it must be capable of landing in a 9-knot, 90° crosswind. The maximum demonstrated crosswind component is published in the AFM/POH" 20. The Warrior's placard: "DEMONSTRATED CROSSWIND COMPONENT 20 MPH" 21. Beyond 20 mph no one has demonstrated the landing, and the pilot is testing the airplane.

The technique is part of the number

Published short-field and soft-field performance assumes the manual's technique exactly. The Warrior's takeoff chart names the flap setting and the rotation speed for each line 1. Its landing chart names 40 degrees of flap, power off, maximum braking, and 73 mph 4. The Airplane Flying Handbook's short-field lift-off: "an attempt to pull the airplane off the ground prematurely, or to climb too steeply, may cause the airplane to settle back to the runway or make contact with obstacles" 22. Five mph fast on the approach adds distance no chart shows.

Flaps

Takeoff flaps shorten the ground roll and flatten the climb. The Warrior's chart gives rotation at 52 mph with 25 degrees of flap and 65 mph with none, and a shorter roll with flaps 1. Landing flaps steepen the approach and slow the touchdown. The landing chart assumes 40 degrees 4. The flap setting on the airplane must match the flap setting on the chart, or the chart's number does not apply.

Surface and slope

Grass, soft, wet, or contaminated runways add roll. The handbook: "Typically, performance chart information assumes paved, level, smooth, and dry runway surfaces," and "Any surface that is not hard and smooth increases the ground roll during takeoff" 23. The pamphlet: "long grass, sand, mud, or deep snow can easily double your takeoff distance" 13. Where the manual gives a correction factor, the pilot uses it. The Warrior's manual gives none, so the 50 percent margin covers the estimate. The pilot does not take off from a wet grass strip at gross weight.

Slope matters in both directions. The handbook: "An upsloping runway impedes acceleration and results in a longer ground run during takeoff. However, landing on an upsloping runway typically reduces the landing roll. A downsloping runway aids in acceleration on takeoff resulting in shorter takeoff distances. The opposite is true when landing, as landing on a downsloping runway increases landing distances" 23. The uphill takeoff and the downhill landing each lengthen the critical distance. The Chart Supplement lists the slope.

Ground effect reduces induced drag within about a wingspan of the surface. The handbook: "When the wing is at a height equal to its span, the reduction in induced drag is only 1.4 percent. However, when the wing is at a height equal to one-fourth its span, the reduction in induced drag is 23.5 percent and, when the wing is at a height equal to one-tenth its span, the reduction in induced drag is 47.6 percent" 24. The danger is at takeoff: "In extreme conditions, such as high gross weight, high density altitude, and high temperature, a deficiency of airspeed during takeoff may permit the aircraft to become airborne but be incapable of sustaining flight out of ground effect" 24. An overloaded or high-density-altitude airplane can lift off in ground effect and still be unable to climb out of it.

Stall speed and load factor

Stall speed rises with the square root of the load factor. The handbook: "The load factor for any aircraft in a coordinated level turn at 60° bank is 2 Gs," and "an aircraft's stalling speed increases in proportion to the square root of the load factor" 25. The square root of 2 is 1.41, so a 60-degree level turn raises the stall speed about 41 percent. The handbook's second example: "banking an aircraft greater than 72° in a steep turn produces a load factor of 3," and an airplane that stalls at 45 knots "must be kept greater than 75 knots to prevent inducing a stall" 26.

Va falls with weight

Maneuvering speed decreases as weight decreases. The handbook: "It is important to consider weight when referencing this speed. For example, VA may be 100 knots when an airplane is heavily loaded, but only 90 knots when the load is light" 27. A light airplane reaches the limit load factor at a lower speed because the same gust or pull produces more acceleration on less mass. A lightly loaded airplane has a lower Va, not a higher one.

Stall speed rises with weight

Stall speed rises with weight, and each table carries a weight. The Warrior's manual: "Stall speed at a gross weight of 2325 pounds with power off and full flaps is 58 miles per hour," and "Stall speeds at lower weights will be correspondingly less" 28. The takeoff chart, the landing chart, and the climb chart each carry "GROSS WEIGHT 2325 LBS" in the title block 1 4 29. Above that weight there is no chart.

The flight of N1651J

On August 12, 2021, at 7 in the evening, a Piper Cherokee 140 took off from Panguitch, Utah, with three people aboard. The airplane could not climb. The pilot made a forced landing in the terrain ahead, the airplane struck a fence, and nobody was hurt. The pilot was a 38-year-old airline transport pilot with 9,429 hours, 22 of them in the type. The Cherokee's certified gross weight was 2,100 pounds 30.

The pilot "conducted a maximum performance takeoff by adding full power and holding the brakes until engine RPM stabilized. The pilot released the brakes, and upon reaching rotation speed, the airplane drifted left. He maneuvered the airplane toward the runway centerline, and it touched down onto the runway briefly before it became airborne again. The airplane ascended to about 100 ft above ground level, before it began descending. The pilot stated that, there was no available runway remaining, so he initiated a forced landing to the uneven terrain ahead. During the landing roll, the airplane struck a fence and vegetation substantially damaging the fuselage" 30.

The pilot computed the weight. "The pilot reported that prior to takeoff, he calculated the airplane's weight with passengers and fuel, and determined it to be about 20 pounds under the maximum gross weight of the airplane. However, the pilot did not conduct preflight performance calculations prior to takeoff" 30. The chart he did not open ends at 7,000 feet: "The pilot operating handbook take-off distance vs. density altitude chart states 'extrapolation of chart above 7,000 ft. [density altitude] is invalid. The calculated density altitude at the time of the accident was 9,000 ft mean sea level (msl)" 30.

The probable cause: "The airplane's inability to maintain altitude during the initial climb due to a degradation in the airplane's performance due to high-density altitude conditions. Contributing to the accident was the pilot's failure to conduct preflight performance planning calculations" 30. The pilot told the NTSB that "if he took more time in preflight preparations, he would have noticed that the density altitude was too high to takeoff" 30.

Where the pilot could have prevented the accident

A 9,000-hour pilot did the weight computation and not the performance computation. Each decision below is marked with the PAVE category that applied to it.

Weight times arm equals moment, and the center of gravity is total moment divided by total weight. The Pilot's Handbook: "If the weight of any object or component is multiplied by the distance from the datum (arm), the product is the moment," and the computation's last step is "To determine the CG, divide the total moment by the total weight" 31. The arithmetic is:

• each item's weight, multiplied by its arm, is its moment
• the pilot adds the weights, and adds the moments
• the total moment, divided by the total weight, is the CG in inches aft of the datum.

The datum

The datum is the manufacturer's reference line, and each arm is the distance from it. The handbook: "Datum (reference datum)—an imaginary vertical plane or line from which all measurements of arm are taken. The datum is established by the manufacturer" 32. The Warrior's manual: "The datum used is 78.4 inches ahead of wing leading edge at the intersection of the straight and tapered section" 33. The datum is ahead of the airplane, so each arm in the Warrior's loading graph is a positive number 34.

Basic empty weight

Basic empty weight includes the unusable fuel and, in the modern format, full oil. The handbook's standard empty weight "consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the aircraft, including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil," and the basic empty weight adds the optional equipment installed 32. The Warrior's manual, older than that format, says the same: "Basic weight consists of the empty weight of the aircraft plus the unusable fuel and full oil capacity" 35. The pilot confirms what the airplane's figure includes before using it. Oil counted twice is an error of the whole sump's weight.

The airplane's own record

The legal source of the empty weight and moment is the airplane's current weighing record and equipment list, not the manual's sample problem. The handbook: "Sample loading problems in the AFM/POH are intended for guidance only; therefore, each aircraft must be treated separately" 31. The Warrior's manual: "The current values should always be used. Whenever new equipment is added or any modification work is done, the mechanic responsible for the work is required to compute a new basic weight and basic C.G. position and to write these in the aircraft log book" 35.

The school's Warrior carries its record in the manual. After an avionics change in 1989 the empty weight went from 1,442.1 to 1,436.7 pounds and the arm from 86.8 to 86.6 inches. The useful load became 888 pounds 6. The sheet in the airplane is the legal record, and the newest sheet is the current one.

Useful load

Useful load is the maximum weight minus the basic empty weight. The handbook: "Useful load—the weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. It is the basic empty weight subtracted from the maximum allowable gross weight" 32. In the school's Warrior the useful load is 2,325 minus 1,437, or 888 pounds 6.

Full fuel is 48 usable gallons at 6 pounds, or 288 pounds 36. Two 170-pound people in front are 340. The loading leaves 260 pounds for the back seats and the baggage bay. The manual's warning: "you cannot fill the airplane with the maximum number of adult passengers, full fuel tanks and maximum baggage" 35.

Six and seven and a half

Avgas weighs 6 pounds per gallon. Oil weighs 7.5. The handbook's standard weights: "Gasoline 6 lb/US gal" and "Oil 7.5 lb/US gal," with the note that "These weights should not be used if actual weights are available" 32. The handbook's other sentence about fuel: "Thirty gallons of fuel may weigh more than one passenger" 37.

Ramp weight and landing weight

Some manuals distinguish ramp weight from takeoff weight. The handbook: "Maximum ramp weight—the total weight of a loaded aircraft including all fuel. It is greater than the takeoff weight due to the fuel that will be burned during the taxi and run-up operations" 32. The difference is the taxi and runup allowance. Some types also set a maximum landing weight below the maximum takeoff weight: "Maximum landing weight—the greatest weight that an aircraft is normally allowed to have at landing" 32. When a type does, the fuel burned en route is part of the landing plan. The Warrior has one maximum weight for both, 2,325 pounds 33.

The loading envelope chart shows whether the loading is legal. The Warrior's chart plots weight against the CG in inches aft of the datum. The normal category envelope starts at 83.0 inches and 1,950 pounds. From there it runs 38:

• up a sloping line to 87.0 inches at 2,325 pounds
• flat across to 93.0 inches
• down the 93.0-inch line.

The limits table gives the same numbers: 87.0 to 93.0 inches at 2,325 pounds, and 83.0 to 93.0 at 1,950 pounds 33. The pilot plots the loaded point. Inside the line, the loading is legal. On or outside the line, the pilot changes the loading.

Fuel burn moves the point

Fuel burn moves both weight and CG in flight. A loading that is legal at takeoff can leave the envelope later, so the pilot checks both the takeoff condition and the landing condition. The handbook: "Fuel burn can also affect the CG based on the location of the fuel tanks. For example, most small aircraft carry fuel in the wings very near the CG and burning off fuel has little effect on the loaded CG" 39. In the Warrior the fuel sits at 95 inches, aft of the 93.0-inch aft limit, so burning fuel moves the point forward as it moves it down 34. A point near the forward line at takeoff is nearer it at landing, and a point near the aft line at takeoff is at its worst at takeoff.

The weight-shift formula

Weight moved, times the distance it moves, equals total weight times the change in CG. The handbook: "When weight is shifted from one location to another, the total weight of the aircraft is unchanged. The total moments, however, do change in relation and proportion to the direction and distance the weight is moved," and "The shifting weight proportion formula can also be used to determine how much weight must be shifted to achieve a particular shift of the CG" 40. In a 2,300-pound airplane, moving a 40-pound bag from the baggage bay to the rear seat moves the CG forward. The change is 40 times the distance moved, divided by 2,300. The formula also solves for the weight: the CG change wanted, times the total weight, divided by the distance available, is the weight to move.

Overweight degrades each number at once

Overweight operation degrades each performance number at once. The handbook's list for an overloaded airplane includes "Higher takeoff speed," "Longer takeoff run," "Reduced rate and angle of climb," "Higher stalling speed," "Longer landing roll," and "Excessive weight on the nose wheel or tail wheel" 41. Above gross weight the structural margin is also reduced, and the performance charts, each drawn at 2,325 pounds, no longer apply 1.

Baggage placards are structural limits

The floor and the tiedowns are certified to the placarded weight. The Warrior's baggage door carries "BAGGAGE MAXIMUM 200 LBS" 21, and the limits table repeats "BAGGAGE CAPACITY 200 LBS" 33. A 250-pound load that keeps the CG inside the envelope is still over the placard, and the placard is a limit under 91.9.

The utility category envelope

Many trainers hold utility category approval only inside a smaller envelope. The Warrior's utility category is 1,950 pounds with CG from 83.0 to 86.5 inches, against the normal category's 2,325 pounds and 93.0-inch aft limit 33. The placards say what that limit means: "UTILITY CATEGORY OPERATION - NO BAGGAGE OR AFT PASSENGERS ALLOWED," and the approved maneuvers are "STEEP TURNS, LAZY EIGHTS, CHANDELLES" at an entry speed of 124 mph, with "SPINS PROHIBITED" 21. The steeper maneuvers are legal only inside the small envelope. Spins are prohibited in this airplane in both categories: "SPINS ARE PROHIBITED FOR NORMAL AND UTILITY CATEGORIES" 42.

A forward CG is more stable and nose-heavy. The handbook: "Loading in a nose-heavy condition causes problems in controlling and raising the nose, especially during takeoff and landing," and exceeding the forward limit "may result in excessive loads on the nosewheel, a tendency to nose over on tailwheel type airplanes, decreased performance, higher stalling speeds, and higher control forces" 39. The forward-loaded airplane needs more flare force, stalls at a higher speed, and cruises slower. The tail holds the nose up against more weight.

Aft CG

An aft CG is less stable and slightly faster in cruise, with degraded stall and spin recovery. The handbook: "Loading in a tail heavy condition has a serious effect upon longitudinal stability, and reduces the capability to recover from stalls and spins. Tail heavy loading also produces very light control forces, another undesirable characteristic" 39. "As the CG moves aft, a less stable condition occurs, which decreases the ability of the aircraft to right itself after maneuvering or turbulence" 39.

Behind the aft limit

A CG behind the aft limit can make spin recovery impossible. North Aero teaches it as the deadliest weight-and-balance error. The Warrior's manual: "If the C.G. is too far aft, the airplane may rotate prematurely on takeoff or try to pitch up during climb. Longitudinal stability will be reduced. This can lead to inadvertent stalls and even spins; and spin recovery becomes more difficult as the center of gravity moves aft of the approved limit" 35. Two heavy people in the back seats at about 118 inches and a full baggage bay at about 143 is the loading to compute first 34.

Operating limitations bind wherever they appear. Section 91.9: "no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards" 43. Each of these carries the same force:

• the Warrior's Section III, the FAA-approved part of the manual
• the placards on the panel and the baggage door
• the arcs on the airspeed indicator.

The airspeed limits

The airspeed limits, in the Warrior's calibrated miles per hour 44:

• Vne, never exceed, 176 mph, the red line
• Vno, maximum structural cruise, 140 mph, the top of the green arc
• Va, maneuvering, 124 mph, on a placard and not on the dial
• Vfe, maximum flaps extended, 115 mph on the later serials, the top of the white arc.

The handbook's markings: the white arc ends at "the maximum speed with the flaps extended," the green arc ends at "the maximum structural cruising speed. Do not exceed this speed except in smooth air," and the red line is the never exceed speed 27. Va has no mark because it changes with weight.

What Va covers

Va covers one thing. The handbook: "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" 45. Below Va, that single input stalls the airplane before it breaks it. The handbook's limit: "Operating at or below design maneuvering speed does not provide structural protection against multiple full control inputs in one axis or full control inputs in more than one axis at the same time" 45. Va does not cover repeated inputs or combined inputs.

The limit load factors

The certified limit load factors, flaps up, by category are normal 3.8 and minus 1.52 g, and utility 4.4 and minus 1.76 g. The handbook's table: "Normal 3.8 to –1.52" and "Utility (mild acrobatics, including spins) 4.4 to –1.76" 46. The Warrior's Section III: "MAXIMUM POSITIVE LOAD FACTOR (Normal Category) 3.8. MAXIMUM POSITIVE LOAD FACTOR (Utility Category) 4.4. MAXIMUM NEGATIVE LOAD FACTOR No inverted maneuvers approved" 44. The structure carries one and a half times the limit before it fails, and the handbook says that reserve "is not something that pilots should willfully abuse" 46.

Vy gives the most altitude per minute. Vx gives the most altitude per distance. The Warrior's manual: "The best rate of climb at gross weight will be obtained at 87 miles per hour. The best angle of climb is at 76 miles per hour" 28. Obstacle clearance planning uses the Vx numbers. The Airplane Flying Handbook's instruction is to hold Vx "until all obstacles have been cleared, or if no obstacles are present, until reaching an altitude of at least 50 feet above the takeoff surface" 22.

The rate falls, and the ceiling

Climb rate falls with altitude. The Warrior's climb chart is drawn at gross weight and 87 mph. It shows about 650 feet per minute at sea level and zero near 15,000 feet of density altitude 29. The handbook defines the ceilings: "the absolute ceiling of an aircraft produces zero ROC. The service ceiling is the altitude at which the aircraft is unable to climb at a rate greater than 100 feet per minute (fpm)" 47. At a 9,000-foot density altitude the Warrior's chart shows about 250 feet per minute at gross weight.

The cruise table

The cruise performance table links power, RPM, true airspeed, and fuel flow at each altitude. The Warrior's cruise chart gives the true airspeed at 55, 65, and 75 percent power against density altitude 48. The range chart gives the fuel: "75% POWER 9.2 GPH. 65% POWER 8.0 GPH. 55% POWER 6.7 GPH" 49. The same table supplies the fuel plan and the nav log's true airspeed.

Range and endurance are different plans

Maximum range and maximum endurance occur at different power settings. The handbook: "Range involves consideration of flying distance, while endurance involves consideration of flying time," and "If maximum endurance is desired, the flight condition must provide a minimum fuel flow" 50. Maximum range is the speed where miles per gallon is best. Maximum endurance is the speed where gallons per hour is least, and it is slower. A pilot holding for weather flies the endurance speed. A pilot who must reach a distant field flies the range speed.

The 50-foot columns

The takeoff and landing charts carry a ground roll and a distance over a 50-foot obstacle. The handbook: "A pilot can also compute distances for a no flap takeoff over a 50 foot obstacle scenario, as well as with flaps over a 50 foot obstacle" 51. The Warrior's charts show both lines 1 4. The obstacle column includes the air segment. The ground-roll column alone understates the runway needed when an obstacle stands off the end. An obstacle always stands off the end.

Tracking actual performance against computed performance is a habit. The pilot notes three comparisons:

• the ground roll against the chart's roll
• the climb rate against the chart's rate
• the fuel burn against the table's burn.

An airplane that is consistently under book needs a bigger margin and a report to maintenance. The handbook's caveat gives the reason: the chart "will not be accurate if the aircraft is not in good working order" 2. An airplane that gives 550 feet per minute where the chart says 650 shows the pilot its margin.

A per-flight event

The performance check is a per-flight event, not a per-airplane fact. A new field elevation, a new temperature, or a new load resets each number. The handbook: "Preflight planning should include a check of performance charts to determine if the aircraft's weight may contribute to hazardous flight operations" 41. The Warrior that left Salinas at sea level in the morning performs differently at a mountain strip in the afternoon. The pilot opens the chart again.

The runway decision is computed

Runway and takeoff path selection is a computed decision. The decision includes:

• the airplane's performance and limitations, from the charts
• the distance available, from the Chart Supplement
• the surface and the slope
• the wind, split into its components
• the pilot's capability, against the demonstrated crosswind.

The pilot makes the decision before taxi, not at the hold-short line. The Airplane Flying Handbook: "The pilot should also consider available options if an engine failure occurs after takeoff. These options include the preferred direction for any emergency turns to landing sites based on the departure path, altitude, wind conditions, and performance" 7. The pilot at Panguitch made the decision at rotation, without opening the chart.