Total Air Temperature — Page 140, Lesson 166

We're starting a fresh topic here: the performance definitions and abbreviations that form the backbone of every take-off, climb, and landing calculation you'll ever do. This is the vocabulary of the entire performance syllabus, so I want to walk you through it methodically. Let's begin with the take-off phase, because that's where most of these speeds live. We have TOD, which stands for Take-off Distance — that's the actual distance the aircraft needs to become airborne and clear an obstacle. Then TODA is the Take-off Distance Available, the physical runway plus any clearway you're allowed to use. TODR is the Take-off Distance Required, what the aircraft actually needs under the conditions. Notice the pattern: Available is what the airport gives you, Required is what the aircraft demands. Next, TOGA is Take-off/Go-around thrust — that's the maximum thrust setting used for take-off and for a go-around. TOR is the Take-off Run, the ground roll distance. TORA is the Take-off Run Available, the runway length you can actually roll on. TORR is the Take-off Run Required. TOSS is Take-off Safety Speed, and TOW is Take-off Weight. Now the critical speeds. V1 is the decision speed — before V1 you can abort the take-off and stop; after V1 you must continue. V2 is the take-off safety speed, the speed you climb at after becoming airborne with an engine failed. V2MIN is the minimum take-off safety speed. V3 is the all engines operating steady initial climb speed. V4 is the all engines operating steady take-off climb speed. Let me continue with the V-speeds that govern the rest of the flight. VA is the Design Manoeuvring Speed. VEF is the assumed speed of engine failure — that's the speed at which we assume the critical engine fails during the take-off calculation. VFE is the maximum flap extended speed. VFR is Visual Flight Rules. VFTO is the final take-off speed. VGO is important: it's the lowest decision speed from which a continued take-off is possible within the TODA with one engine inoperative. VMD is the Velocity of Minimum Drag, and VMP is the Velocity of Minimum Power. VLE is the maximum speed with landing gear extended. VLO is the maximum speed at which the landing gear may be lowered — note the difference, VLO is specifically for the lowering operation. VLOF is the lift-off speed. VMBE is the maximum brake-energy speed — exceed this and the brakes can't absorb the energy. VMC is the minimum control speed with the critical power unit inoperative. Then we have the three control speeds: VMCA is minimum control speed in the air during take-off climb, VMCG is ground minimum control speed at or near the ground, and VMCL is landing minimum control speed on the approach. VMO is the maximum operating speed. VMU is the minimum unstick speed. VNE is the never exceed speed. VP is the hydroplaning or aquaplaning speed. VR is the rotation speed. VRA is the turbulence speed or rough air speed. VREF is the reference landing speed, which replaced the old VAT speed. Now the stall speeds, and these are precise. VS is the stalling speed or minimum steady flight speed at which the aeroplane is controllable. VSR is the reference stalling speed, assumed to be the same as VS1g. VSR0 is the reference stalling speed in the landing configuration. VSR1 is the reference stalling speed in the specified configuration. VS1g is the one-g stall speed at which the aeroplane can develop a lift force normal to the flight path equal to its weight — that's the 1g stall, assumed the same as VSR. VS0 is the stalling speed with flaps at the landing setting, or the minimum steady flight speed controllable in the landing configuration. VS1 is the stalling speed for the configuration under consideration. VSTOP is the highest decision speed that an aeroplane can stop within ASDA. VX is the speed for the best gradient or angle of climb. VY is the speed for the best rate of climb. VZF is the minimum safe manoeuvring speed with zero flap. Finally, the non-speed items. WAT is weight-altitude-temperature. ZFW and ZFM are zero fuel weight and zero fuel mass. Then the Greek symbols: γ is the climb or descent angle, µ is the runway friction coefficient, θ is the aircraft attitude, and ρ is air density. Now, let me tie this together with the figures I have. Look at Figure 14.2 — it shows the relationship of V1 with VMCG and VMBE. The key point is that V1 cannot be allowed to be less than VMCG, because engine failure below VMCG means you can't maintain directional control on the ground. Then Figure 14.3 examines the factors that affect VR, the rotation speed. And Figure 14.4 shows V2, the take-off safety speed. The critical relationship to remember is the Available versus Required distinction — that's the whole game in performance. The runway gives you TORA, TODA, and ASDA; the aircraft demands TORR and TODR. Your job as the pilot is to ensure Required never exceeds Available. And V1 sits at the heart of it, bounded below by VMCG and above by VMBE. That's the framework we'll build every performance calculation on.