02 Performance & Mass & Balance

What is density altitude, and why does it matter operationally?

It is pressure altitude corrected for non-standard temperature; higher density altitude means lower air density and degraded take-off and climb performance.

Which conditions most degrade take-off performance?

High mass, high temperature, high elevation/low pressure, tailwind, upslope and degraded runway condition.

How does a headwind or tailwind affect take-off and landing performance?

Headwind reduces groundspeed for a given airspeed and generally shortens distance; tailwind increases groundspeed and distance significantly.

How does runway slope affect performance?

Upslope generally increases take-off distance and reduces landing distance; downslope does the opposite.

How does increased aircraft mass affect take-off, climb and landing performance?

It increases take-off and landing distances, reduces climb performance and requires higher operating speeds.

Why does excess speed have such a large effect on landing distance?

Kinetic energy is proportional to mass × speed², so a small speed increase produces a disproportionately large increase in energy to dissipate.

What is the practical difference between climb gradient and rate of climb?

Gradient is altitude gained per horizontal distance and is critical for obstacle clearance; rate of climb is altitude gained per unit time.

What primarily determines climb gradient and rate of climb?

Gradient depends mainly on excess thrust/weight; rate of climb on excess power/weight.

Why is OEI climb performance a major transport-aircraft limitation?

Losing one engine removes a large proportion of excess thrust, potentially making climb/obstacle performance limiting even though continued flight is possible.

What is accelerate-stop versus accelerate-go?

Accelerate-stop covers accelerating and rejecting the take-off; accelerate-go covers continuing after the critical engine failure. Performance must satisfy the applicable available distances.

What is the balanced-field concept?

A take-off condition where accelerate-stop and accelerate-go distance requirements are approximately equal.

What is V1 operationally?

The take-off decision speed defining the boundary between stopping and continuing under the applicable certification/performance assumptions.

Why is V1 not simply “the engine-failure speed”?

The critical failure is assumed at VEF before V1; V1 is the decision/action speed used in accelerate-stop and accelerate-go certification.

What is VR?

The speed at which rotation is initiated.

What is V2?

The take-off safety speed associated with required OEI climb performance after lift-off.

Why must VR, V1 and V2 satisfy specific relationships?

They ensure controllability, lift-off capability and required continued-take-off performance after an engine failure.

What is the purpose of reduced-thrust / assumed-temperature take-off?

To use less than maximum available thrust when performance permits, reducing engine wear while preserving required take-off margins.

What is the difference between an assumed-temperature take-off and a fixed derate?

Assumed temperature reduces commanded thrust through performance calculation; a derate selects a lower certified thrust rating.

What factors can limit maximum permissible take-off mass?

Structural mass, runway/field performance, climb performance, obstacle clearance and other aircraft-specific limits.

What factors can limit maximum permissible landing mass?

Structural landing mass and landing-performance requirements.

Why can brake energy become a take-off limitation?

A high-energy rejected take-off must not exceed the certified energy capability of the brakes.

Why does brake-energy demand increase sharply with speed?

The kinetic energy that must be absorbed increases approximately with speed².

What is the difference between gross and net take-off flight path?

Gross represents expected aircraft performance; net applies regulatory margins to provide obstacle-clearance assurance.

Why can an obstacle limit take-off mass even when runway length is sufficient?

The aircraft may have enough runway to become airborne but insufficient climb performance to clear the obstacle with required margins.

What is drift-down after an engine failure?

A controlled descent to an altitude where the aircraft can maintain the required OEI flight condition while preserving terrain clearance.

What is the fundamental mass-and-balance relationship for CG?

CG position = total moment / total mass, using a common datum.

What is a moment in mass and balance?

Mass or weight multiplied by its arm from the reference datum.

What does %MAC express?

CG position as a percentage of the mean aerodynamic chord.

Why must CG remain within the certified envelope?

To maintain adequate stability, controllability, trim capability and structural margins throughout the flight.

What are the main operational effects of a forward versus aft CG?

Forward CG generally increases stability but trim drag and required control force; aft CG reduces trim drag but decreases stability and recovery margin.

Why can an aircraft be within maximum mass but still unsafe to dispatch?

The CG can be outside limits even when total mass is acceptable.

What is Maximum Zero Fuel Mass intended to protect?

Structural loads, especially wing-root bending caused by payload without the bending relief provided by wing fuel.

Why can fuel burn change CG during flight?

Fuel is removed or transferred between tanks located at different arms.

Why can passenger or cargo movement be operationally significant?

It changes aircraft moments and can move the CG outside the permitted envelope.

What is the purpose of a load sheet?

To confirm actual or calculated aircraft mass and CG are within applicable limits for the flight.

What is a Last Minute Change (LMC)?

An approved post-load-sheet change to payload or loading that must remain within defined mass-and-balance limits.

Why must performance calculations use accurate aircraft mass?

Incorrect mass can produce incorrect take-off speeds, thrust settings and runway/climb performance.