T-39 FLIGHT PREPARATION
overboosting the engines at higher altitudes. Safe single engine speed is 133 KIAS.
(Based on takeoff thrust on good engine, maximum weight, gear and flaps up, and
(2) Climb Thrust: Climb performance is based on Maximum Continuous Thrust EPR
Setting for both 1 and 2 engine operation. This is to be used for climb and acceleration
and should not be used for normal operations.
Cruise (Service) Ceiling: Corresponds to a rate of climb of 100 FPM
b. Factors affecting climb performance
(1) Temperature: Variations in outside air temperature from the ICAO standard day
(ISA) have significant affects on time, fuel and distance in climb and performance
(2) Operation of Anti-Ice Systems: The operation of anti-ice systems during climb will
result in decreased climb performance and lower performance ceilings
(3) Engine Loss: The loss of an engine will significantly degrade climb performance
and lower the performance ceilings of the aircraft. Time to climb, fuel to climb, and
distance in climb will all increase, and performance ceiling will be lowered.
a. Factors Affecting Range Performance
(1) Outside Air Temperature: Outside air temperature variations from the ICAO
Standard Day have no effect on range when less than rated power is required. However,
cruise time and fuel flow will be modified slightly because true airspeed and engine fuel
consumption vary with temperature at a given Mach number. These relationships are true
whether cruising at maximum range (climbing flight path) or constant altitude. For
maximum range cruise where rated power is required (such as 1 engine operation), an
increase in temperature means a reduction in range, altitude, Mach number, time, and an
increase in fuel flow. For constant altitude cruise at rated power, an increase in
temperature reduces the maximum allowable weight and Mach number that can be flown
at that altitude.
(2) Wind: When winds are calm, ground speed equals true airspeed. When flying into
a headwind, ground speed equals true airspeed less the headwind component. When
flying with a tailwind the reverse is true. Additionally, wind affects maximum range
values as a result of changes in maximum-range true airspeeds. When striving for
maximum range, it is advantageous to reduce the time of exposure to a headwind
component and increase the time of exposure to a tailwind component.