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Chapter 10 | Performance
VREF : Landing Reference Speed As discussed earlier, the large range of turbine aircraft operating weights results in a corresponding spread of landing speeds. Therefore, there’s no single final approach speed used in large turbine aircraft. Rather, the term VREF is used as landing reference speed. Lest all these new terms sound too mystifying, let’s consider where VREF comes from. Remember your old rule of thumb for calculating final approach speed? VREF for many turbine aircraft is similarly calculated at 1.3 VS0 (1.3 × stall speed in landing configuration). VREF accordingly increases with aircraft weight. A Boeing 727, for example, may weigh anywhere from around 110,000 pounds to 180,000 pounds on final approach. Based upon landing weight, its final approach speed varies from around 112 knots to 147 knots. As with the takeoff V-speeds, pilots must compute VREF for every landing. V2 and engine-inoperative best rate of climb are also recomputed for every landing to allow for engine failure in case of a go-around. Approach climb gradient (climb performance during singleengine go-around) must also be considered for such situations; it’s usually the most restrictive landing performance issue. To determine approach climb gradient, it is necessary to consider the outside air temperature (OAT), airport density altitude, aircraft configuration, and aircraft weight. When determining landing performance, the FAA again requires that minimum standards be met for operations onto any particular runway. Airport density, altitude, wind components, runway surface conditions, and slope must be considered, along with aircraft configuration and weight, when determining required field length and maximum landing weight. The FAA requires most categories of aircraft to be able to land safely within 60 percent of the landing distance available at the primary destination airport. (Seventy percent is allowed for filed alternate airports.)
Braking Performance One additional factor to consider on both takeoff and landing performance calculations is the aircraft’s braking system. This is very important because all deceleration and stopping performance is predicated on use of wheel braking only. (Thrust reverser performance does not enter into the calculations, even
though the effects may be great. Consider reversers as adding to the margin of safety.) Braking charts are provided for crew reference on larger turbine aircraft.
Routine Performance Planning We’ve now covered most of the performance issues unique to turbine aircraft operations. The performance charts and graphs themselves, which you’ll see in ground school, are similar to those you’ve used in the past for piston or military aircraft. But all of those performance calculations can be a lot of work! When aircraft are delivered to corporate or airline flight departments, they come with manufacturers’ performance charts. These charts tend to be very complex and too time-consuming for flight crews to use routinely. Therefore, most flight departments develop quick reference performance charts for their flight crews. Quick reference charts are particularly valuable for regularly scheduled operations, which often may include “ten-minute quick turns” and nine or more flying legs per day.
TOLD Cards Two types of quick reference charts are particularly common among operators. Most f light departments construct simple quick reference Takeoff and Landing Data cards (TOLD cards), allowing flight crews to quickly determine aircraft V1, VR , V2 , and engine-inoperative best rate of climb for takeoff, as well as VREF, V2 , and engine-inoperative best rate of climb for landing (Figure 10.3). Using TOLD cards, these airspeeds may be quickly calculated for a given aircraft based upon gross weight, flap position, and sometimes other conditions. On new technology aircraft, computers are often used to calculate these airspeeds, along with power settings and other flight parameters.
Airport Analysis Tables To deal with airport-specific performance computations in a safe and timely manner, all air carriers and many corporate flight departments enlist the aid of specialized companies or computer programs to prepare performance data for every likely situation. This
