The outside temperature drops as the altitude rises (roughly 2 degrees C per 1000 feet). The following parameters influence engine performance. The outside air pressure (altitude), aircraft's speed, outside temperature and bleed need all influence the engine performance. Safety of flight is affected by all these factors.
In normal conditions, an altitude increase can have two effects. A decrease in air pressure causes thrust to decrease. A decrease in temperature tends towards increasing thrust. Combining both of these causes a net decrease to thrust. The dominant influence of pressure is predominant
The atmosphere's lower layer may be affected by the weather and geography. Each takeoff will be free from the standard atmosphere.
If the altitude rises, then a temperature increase can be achieved. This is temperature inversion.
An increase in altitude can cause thrust to decrease more than usual. The effect of temperature and pressure both play a role in this decrease.Temperature Inversion
Influence on performance of aircraft
The DISA constant during climb is the basis of certified takeoff performance. The climb performance may be affected by temperature inversion.
A temperature inversion can affect aircraft performance but must be combined other factors.
Inversions will not affect normal takeoffs with all engines running, as the aircraft's performance is already well above the minimum.
This could affect the aircraft's performance only in the case of an engine failure during takeoff.
FAR/JAR 25 rules introduce conservatism in aircraft certification performance to account for inaccuracy in data used for performance calculations. This inaccuracy can also include temperature inversions.
In this case, temperature inversion is unlikely to occur during takeoff.
V1 is the location of the engine failure.
- Maximum takeoff thrust is used.
OAT is close to T.REF or higher, and
- Obstacles can limit the takeoff weight.
- A temperature inversion causes the regulatory net flight path margin to be cancelled
it allows you to fly lower than the required net flight path.
In all other cases, even though performance is affected (inversion over T.REF), there will be no adverse effect if climb performance falls below the nominal one.
The minimum climb gradient at 35 ft above runway is required for the second segment oneengine-inoperative.
For twin-engine aircraft, - 2.4 %
4 % on four-engine aircraft
The net and gross flight paths are separated by:
Twin-engine aircraft: - 0.8 %
For four-engine aircraft, the rate is 1 %
The following graph will show the effect of a temperature inversion (10degC) between 1500 ft and the ground.
The first graph shows an A320 with CFM engine. The effect of temperature inversion on engine thrust is very similar regardless of type.
This is approximately 10 % thrust reduction with a 10 degC conversion. The twin-engine aircraft will have the same effect on the climb performance as the single-engine model.
The graph depicts the gross trajectory after an engine failure at V1. It is limited to the minimum second segment climb gradient and a normal temperature variation with the altitude (-3degC). The curve B indicates the net flight path.
The curve C shows the gross path with a 10degC Inversion from ground to 1500ft.Airbus Takeoff Performance
The graph indicates that the temperature inversion of 10degC and engine failure at V1 are safe conditions. Although the gross climb gradient may be affected, it is not a cause for concern.
If an engine failure occurs later in takeoff, it will give you additional margin because you have more climb time with all engines running.