Aircraft Performance

For instance, a pilot is downwind for runway 18, and the Performance Speeds tower asks if runway 27 could be accepted. There is a light True airspeed (TAS)—the speed of the aircraft in relation to rain and the winds are out of the east at ten knots. The pilot the air mass in which it is flying. accepts because he or she is approaching the extended centerline of runway 27. The turn is tight and the pilot must Indicated airspeed (IAS)—the speed of the aircraft as descend (dive) to get to runway 27. After becoming aligned observed on the ASI. It is the airspeed without correction for with the runway and at 50 feet AGL, the pilot is already 1,000 indicator, position (or installation), or compressibility errors. feet down the 3,500 feet runway. The airspeed is still high by about ten percent (should be at 70 knots and is at about Calibrated airspeed (CAS)—the ASI reading corrected for 80 knots). The wind of ten knots is blowing from behind. position (or installation) and instrument errors. (CAS is equal to TAS at sea level in standard atmosphere.) The color First, the airspeed being high by about ten percent (80 knots coding for various design speeds marked on ASIs may be versus 70 knots), as presented in the performance chapter, IAS or CAS. results in a 20 percent increase in the landing distance. In performance planning, the pilot determined that at 70 Equivalent airspeed (EAS)—the ASI reading corrected knots the distance would be 1,600 feet. However, now it for position (or installation), for instrument error, and for is increased by 20 percent and the required distance is now adiabatic compressible flow for the particular altitude. (EAS 1,920 feet. is equal to CAS at sea level in standard atmosphere.) The newly revised landing distance of 1,920 feet is also V —the calibrated power-off stalling speed or the minimum affected by the wind. In looking at Figure 11-19, the affect S0 steady flight speed at which the aircraft is controllable in the of the wind is an additional 20 percent for every ten miles landing configuration. per hour (mph) in wind. This is computed not on the original estimate but on the estimate based upon the increased V —the calibrated power-off stalling speed or the minimum airspeed. Now the landing distance is increased by another S1 steady flight speed at which the aircraft is controllable in a 320 feet for a total requirement of 2,240 feet to land the specified configuration. airplane after reaching 50 feet AGL. V —the speed at which the aircraft obtains the maximum That is the original estimate of 1,600 under planned conditions Y increase in altitude per unit of time. This best ROC speed plus the additional 640 feet for excess speed and the tailwind. normally decreases slightly with altitude. Given the pilot overshot the threshhold by 1,000 feet, the total length required is 3,240 on a 3,500 foot runway; 260 V —the speed at which the aircraft obtains the highest feet to spare. But this is in a perfect environment. Most pilots X altitude in a given horizontal distance. This best AOC speed become fearful as the end of the runway is facing them just normally increases slightly with altitude. ahead. A typical pilot reaction is to brake—and brake hard. Because the aircraft does not have antilock braking features V —the maximum speed at which the aircraft can be safely like a car, the brakes lock, and the aircraft hydroplanes on LE flown with the landing gear extended. This is a problem the wet surface of the runway until decreasing to a speed of involving stability and controllability. about 54 knots (the square root of the tire pressure (√36) × 9). Braking is ineffective when hydroplaning. V —the maximum speed at which the landing gear can LO be safely extended or retracted. This is a problem involving The 260 feet that a pilot might feel is left over has long since the air loads imposed on the operating mechanism during evaporated as the aircraft hydroplaned the first 300–500 feet extension or retraction of the gear. when the brakes locked. This is an example of a true story, but one which only changes from year to year because of new V —the highest speed permissible with the wing flaps in a participants and aircraft with different N-numbers. FE prescribed extended position. This is because of the air loads imposed on the structure of the flaps. In this example, the pilot actually made many bad decisions. Bad decisions, when combined, have a synergy greater V —the calibrated design maneuvering airspeed. This is than the individual errors. Therefore, the corrective A the maximum speed at which the limit load can be imposed actions become larger and larger until correction is almost (either by gusts or full deflection of the control surfaces) impossible. Aeronautical decision-making is discussed more without causing structural damage. Operating at or below fully in Chapter 2, Aeronautical Decision-Making (ADM). 11-18