1.01 Aircraft Performance Requirements: Take-off, En Route and Landing

1.1.1 Introduction

01. General

Performance requirements form part of the airworthiness requirements. Together with associated operational rules they are intended to ensure a satisfactory safety level in civil aviation as far as performance of the aircraft is concerned.

All company aircraft have been certified according to the US rules for turbine aircraft. These rules, formerly known as “Special Regulation 4223”, are now incorporated in Federal Aviation Regulations Part 25. The associated operational rules are contained in FAR 121.

The authority normally follows the US requirements. Upon issuing a certificate of airworthiness the authority may impose additional requirements, or grant dispensation from certain US regulations.

If it is deemed necessary, the company may also impose more restrictive directives.

The following terms and concepts are applied in the performance requirements.

Temperature

The effect of the ambient temperature must be taken into account fully, except for the determination of the required landing runway length for dispatch.

Humidity

Turbine aircraft performance is based on an arbitrarily selected humidity. Deviations from this reference humidity have a minor effect on performance and are not accounted for.

Climb gradients

Climb requirements are specified in terms of climb gradients.

A climb gradient is the ratio, in the same units, expressed as a percentage of:

change in height / horizontal distance travelled

Example: 200 ft height gained over a distance of 10,000 ft = a climb gradient of 2%.

Gross performance is the performance of the aircraft as established from the certification tests.

Net performance is the gross performance adjusted to include a certain performance margin to cover unfavourable deviations.

Example: Gross take-off flight path gradient minus gradient margin = net take-off flight path gradient.

1.1.2 Take-off Speeds

01. Minimum Control Speed, V_MC

V_MC is the minimum speed, at which, when the critical engine is suddenly made inoperative, it is possible to recover control and to maintain straight flight at that speed, with an angle of bank not in excess of 5°.

V_MC values are determined for:

• operation on the ground: V_MC – Ground
  This speed is demonstrated with the landing gear extended but without use of brakes or nose wheel steering (except for DC-8-50 where rudder pedal nose wheel steering is accounted for under good runway friction conditions). It is used for setting a lower limit for V₁.
• operation in the air: V_MC – Air
  This speed is demonstrated with the landing gear retracted and away from the ground effect. It may govern the lowest value for V_R or V_{2 min}.

V_MC mainly depends on the ability of the rudder and ailerons to counteract the yawing moment resulting from the asymmetric thrust condition. V_MC decreases with decreasing thrust.

Note: For engine-out handling, see guide 1.3.

02. Take-off Decision Speed, V₁

This speed is used to identify the power failure point at which, for the purpose of determining the required runway length, sudden and total power loss of the critical engine is assumed to occur.

In actual operation this speed is used as a “go” or “no go” parameter.

V₁ is selected by the manufacturer, but should neither be less than V_MC – ground, nor more than V_R. For further details, see 1.1.3 Take-off Field Length.

03. Rotation Speed, V_R

V_R is the speed at which rotation to the lift-off attitude is to be initiated.

If the rotation is too late and/or too little, the aircraft will pass low over the end of the runway at a speed in excess of V₂.

If the rotation is too early and/or too much, drag is increased and acceleration will be affected unfavourably, so that also in this case the aircraft will pass low over the end of the runway. In both cases potential performance may be wasted to such an extent that safety is impaired. (See Fig. 1.)

V_R is selected by the manufacturer and shall comply with the following provisions:

V_R shall not be less than:

• V₁;
• 1.05 V_MC;
• a speed which permits attainment of V₂ prior to reaching 35 ft height above the take-off surface.

Furthermore certain lift-off criteria must be met.

04. Take-off Climb Speed, V₂

This is the speed selected by the manufacturer, at which the weight limitations resulting from the second segment climb requirement have been assessed. It should not be less than V_{2 min}, nor less than V_R plus the increment in speed attained prior to reaching a height of 35 ft above the take-off surface.

Note: V_{2 min} (minimum take-off climb speed) is the greater of 1.2 V_MC and 2.1 V_MC Air.

1.1.3 Take-off Field Length

01. Airport Terms

Runway: This is a defined rectangular area, selected or prepared for the normal take-off and landing run of an aircraft.

Stopway: This is an area extending beyond the runway, meeting the following requirements:

• not less in width than the runway it augments;
• designated by the airport authorities for use in decelerating the aircraft during a rejected take-off;
• capable of supporting the aircraft during a rejected take-off without inducing structural damage to the aircraft.

Note: From this definition it will be clear that a stopway may only be taken into account for take-off and not for landing.

Clearway: A clearway is an area extending beyond the runway, meeting the following requirements:

• not less than 500 ft wide;
• under the control of the airport authorities.

The clearway shall be regarded as a plane, extending from the end of the runway, with an upward slope not in excess of 1.25% above which no ground or objects shall project.

Note: For the purpose of establishing take-off distances (35 ft height point), the clearway plane is considered to be take-off surface.

Company policy: Only in very incidental cases stopways and/or clearways that are available and considered safe for use, are taken into consideration when working out take-off weight limitations published in TL-Charts.

02. Minimum Required Take-off Runway Length

The minimum required take-off runway length is the longer of the following distances:

A. Accelerate-stop distance

This is the sum total of:

• the distance required to accelerate the aircraft from a standing start to V₁ with all engines operating, and
• the distance required to bring the aircraft to a full stop from the speed V₁.

This sum total is established on a smooth, hard and dry runway surface as follows:

• centre of gravity: most unfavourable position within allowable range;
• slats/flaps: take-off position throughout;
• gear: extended throughout;
• acceleration to V₁: all engines at maximum take-off thrust from the brakes;
• deceleration from V₁: suitable time delay before taking decision, thereafter, remaining engines closed down to idling thrust;
• maximum allowable wheel braking;
• other approved means of braking (e.g. spoilers).

B. Take-off distance with an engine failure

This is the sum total of:

• the distance required to accelerate the aircraft from a standing start to V₁ with all engines operating, and
• the distance required to continue the take-off and reach 35 ft height above the take-off surface, with failure of the critical engine at V₁.

This sum total is established on a smooth, hard and dry runway surface as follows:

• centre of gravity: most unfavourable position within allowable range;
• slats/flaps: take-off position throughout;
• gear: retracting after becoming airborne;
• acceleration to V₁: all engines operating at maximum take-off thrust from the brakes;
• acceleration beyond V₁: remaining engines at take-off thrust;
• prescribed take-off technique.

C. All engine take-off runway length

This is 115% of the horizontal distance along the take-off path from the start of the take-off to 35 ft height above the take-off surface, with all engines operating, this distance being established as follows:

• centre of gravity: most unfavourable position within allowable range;
• slats/flaps: take-off position throughout;
• gear: retracting after becoming airborne;
• acceleration: all engines at maximum take-off thrust from the brakes;
• prescribed take-off technique.

03. Rejected Take-off

3.1 General

Definition: A take-off that is discontinued after take-off thrust is set and initiation of the take-off roll has begun.

The Rejected Take-Off (RTO) is a maneuver performed during the take-off roll if the flight crew determines that the take-off should not be continued. Most RTOs (approximately 95%) are initiated at speeds below 100 knots and are executed without incidents. However the potential for an accident or incident following a high speed RTO remains high. A review of the available data over the history of western built transport jet operations shows that approximately one in 3,000 take-offs has been rejected. Of these RTOs about one in 1,000 was unsuccessful, resulting in an overrun accident or incident. That is an accident/incident rate of one per 3,000,000 take-off attempts.

From the above statistics one can conclude that:

• An RTO is not a very common event.
• The probability of an RTO incident/accident is remote.
• The infrequency of RTO events may lead to an ease off with regard to maintaining sharp decision-making skills.

In spite of these statistics pilots should be prepared to make the correct go / no go decision on every take-off.

Note: V₁ is the maximum speed at which the RTO maneuver can be initiated and the aircraft stopped within the remaining field length under the conditions and procedures defined in the FARs / JARs.

It is the latest point in the take-off roll where a stop can be initiated. If an engine failure is recognized before V₁ an abort can be made within the remaining runway. If an engine failure is recognized at or after V₁, the take-off can be continued within the remaining take-off distance.

V₁ is the end of the go / no go decision process, not the beginning.

3.2 Factors Influencing Stopping Distance

Braking

If available, autobrakes must be set to the RTO mode before the take-off. The proper braking sequence for a RTO at V₁ is clearly different from a normal landing.

Braking has top priority and provides the primary stopping forces, followed by spoilers and reverse thrust.

Note: If autobrakes are not available the proper braking technique during an RTO is to apply full brake pedal force and maintain full brake pedal force until the aircraft comes to a complete stop.

Autobrakes are not available below a specified aircraft speed value (usually 85-90 knots).

The PNF must monitor the autobrake system and advise the PF if a failure occurs.

On some aircraft types dispatch is possible with the antiskid system inoperative. This represents a special case for brake application techniques. In this situation the pilot executing the RTO should apply steady moderate pedal pressure consistent, in his judgement, with runway conditions, aircraft dispatch weight and the available runway length. Full brake pressure should not be applied with the antiskid system inoperative due to the risk of tire failure.

To minimize the possibility of skidding a tire, which can lead to a blowout, the speedbrakes / spoilers should be deployed before brakes are applied. This provides the highest possible wheel loads to keep the wheels rotating with the forward motion of the aircraft.

Runway line-up

Correct runway line-up technique should always be applied regardless of whether or not there is excess runway available.

The V₁ call

One important factor in avoiding RTO overrun accidents is to recognize reaching V₁ when the aircraft actually does reach V₁. The PF cannot react properly to V₁ unless the V₁ call is made in a timely, crisp and audible manner. When V₁ is reached this call out must be finished.

3.3 Stop and Go Options

When performing a take-off at a field length limit weight, the pilot is assured that the aircraft performance will, at the minimum, conform to the requirements of the FARs / JARs. This means that the take-off can be rejected prior reaching V₁ and the aircraft stopped before the end of the runway, or if the take-off is continued, a minimum height of 35 feet will be reached over the end of the runway. This section discusses some effects when deviating from the minimum requirements.

The horizontal axis of figure 1 is the incremental speed in knots above V₁ at which a maximum effort stop is initiated. Typically at V₁, the aircraft is accelerating at 3 to 6 knots per second. This means that a ‘STOP’ call made at V₁ results in a minimum speed of 80 knots at which the aircraft would cross the end of the runway, assuming the pilot used all of the transition time allowed in the Aircraft Flight Manual (AFM) (approximately three seconds depending on aircraft type) to reconfigure the aircraft to the stop configuration, and that a maximum stopping effort was maintained.

V_EF is the speed at which the AFM calculation assumes the engine to fail (a minimum of one second before reaching V₁). The horizontal axis of figure 2 shows the number of knots prior to V_EF that the engine actually fails, and the vertical axis gives the ‘screen height’ achieved at the end of the runway. A typical range of acceleration is 3 to 6 knots per second, so the shaded area shows the range in screen height that might occur if the engine actually failed ‘one second early’, or approximately two seconds prior to V₁. In other words, a go decision made with the engine failure occurring two seconds prior to V₁ will result in a screen height of 15 to 30 feet for a field length limited take-off weight.

3.4 Decisions and Procedures

The rejection of a take-off should be restricted to:

• Aural warnings (configuration warning siren, caution beeper, fire bell).
• Engine failure.
• Control problems affecting safe aircraft handling.

The rejection of a take-off is initiated by the call ‘STOP’. In the above mentioned cases both pilots may call ‘STOP’. In all other cases the decision to initiate the rejection of a take-off is restricted to the captain.

Once the rejection is initiated, it must be completed. As the speed approaches V₁ a decision to stop is recommended only for an engine failure / fire or a malfunction which impairs the safety of flight.

To reduce decision time, system malfunctions, which do not affect flyability should be systematically disregarded as the speed approaches V₁.

In order not to distract the attention of the cockpit crew during the rejection of a take-off, no information about the reason to reject will be given until the aircraft has come to a complete stop.

An RTO from close to V₁ speed encountered at high elevation airports and/or at very high temperatures will require the brakes to absorb a significant amount of energy during the stop. After a high energy stop is made, the first officer or flight engineer must monitor brake temperatures (if possible) in order to recognize the possibility of a brake/tire fire.

If a high speed RTO is performed the tower should immediately be advised that the aircraft is still on the runway, that a high energy stop was made, and that emergency equipment is requested to observe the tires and brakes for possible fires.

1.1.4 Take-off Flight Path

01. Principle

After lift-off with the critical engine inoperative, the aircraft must:

1. meet specified climb gradient requirements to ensure adequate climb performance (“airworthiness” requirement);
2. clear all obstacles in a defined area beyond the end of the runway by a safe margin (“operational” obstacle clearance requirement).

For demonstrating compliance with requirement A the “gross” take-off flight path concept is utilized and for requirement B the “net” take-off flight path.

02. The “Gross” Take-off Flight Path

The “gross” take-off flight path may be considered to extend from lift-off to:

• the point where a height of 1500 ft above the take-off surface is reached, or (when higher)
• the point where the transition from the take-off to the clean configuration is completed and the speed for compliance with the “final take-off” climb requirement is reached.

The “gross” take-off flight path is based on the following:

• the aircraft is accelerated on the ground to V₁, at which point the critical engine is made inoperative and remains inoperative during the remainder of the take-off;
• prescribed take-off technique (rotation, reaching V₂ at the 35 ft height point);
• except for gear retraction the configuration shall not be changed before reaching a height of at least 400 ft above the take-off surface;
• between the 35 ft and the 400 ft height points the speed shall be V₂;
• the slope of the airborne portion of the take-off path shall not be negative at any point;
• at each point along the take-off path after reaching 400 ft the available climb gradient shall not be less than the gradient required in the final segment (see sub 03.).

Within the scope of these directives, changes in configuration and speed can be made. The take-off path is then divided into a number of consecutive segments related to changes in configuration and speeds.

03. Climb Requirements

With the landing gear extended (1st segment)

In the configuration existing along the one-engine-out gross take-off flight path between lift-off and the point where the gear is fully retracted, the steady climb gradient without ground effect shall be:

• positive for two-engined aircraft;
• not less than 0.3% for three-engined aircraft;
• not less than 0.5% for four-engined aircraft.

With the landing gear retracted (2nd segment)

In the configuration existing along the one-engine-out gross take-off flight path at the point where the gear is fully retracted, the steady climb gradient without ground effect shall not be less than:

• 2.4% for two-engined aircraft;
• 2.7% for three-engined aircraft;
• 3.0% for four-engined aircraft.

Final take-off (final segment)

In the en-route configuration at the end of the one-engine-out gross take-off flight path, the steady climb gradient shall not be less than:

• 1.2% for two-engined aircraft;
• 1.5% for three-engined aircraft;
• 1.7% for four-engined aircraft.

The above requirements should be met in still air.

04. The “Net” Take-off Flight Path

This begins at a height of 35 ft above the take-off surface at the end of the required runway length and represents the aircraft’s take-off path as outlined in the foregoing subpara reduced by:

• 0.8% climb gradient for two-engined aircraft, or
• 0.9% climb gradient for three-engined aircraft;
• 1.0% climb gradient for four-engined aircraft.

Note: For the portion of the take-off path where the aircraft is accelerated in level flight, the prescribed reduction in climb gradient is applied as an equivalent reduction in acceleration.

05. Take-off Flight Path Obstacle Clearance Requirements

Legal Requirements

According to the legal requirements the net take-off flight path is checked for obstacle clearance up to and including the acceleration segment, assuming:

• an engine failure at V₁ (in fact: engine failure recognition speed)
• an engine failure departure, which is either straight-out from the runway or following the special engine failure procedure as specified at the bottom of the Take-off Weight Limitations (TL) Table.

When the planned track deviates from the extended runway centre line to avoid obstacles (special engine failure procedure), a turn may not be initiated before reaching a height of 50 ft and the maximum bank angle must not exceed 15°. The planned bank angle must be accounted for in the performance calculations.

Vertical clearance must be at least 35 ft above all obstacles lying within an area of at least 90 m + 0.125 D on either side of the planned track (fig. 6). “D” is the distance measured from the end of the take-off distance available.

In the following cases the lateral clearance need not be more than resp. 300 m, 600 m or 900 m and obstacles on either side of the intended track at a distance greater than the above-mentioned need not be cleared.

Company Policy

The company determines obstacle clearance according to the legal requirements as outlined before, however the lateral distance (90 m + 0.125 D) is never limited to less than 900 m.

Furthermore, 300 ft is normally applied as minimum turning height (i.e. 50 ft), but in specific cases lower heights may be used. This will be mentioned on the TL table.

A detailed analysis on obstacle clearance after clean-up will not be performed, however in some cases, when dictated by surrounding terrain, obstacle clearance will be considered.

Complicated engine failure procedures are established in concert with the chief pilot.

Operational Application

The above is all based on engine failure at V₁. An engine failure after V₂ will show an improved obstacle clearance due to the added energy of one engine between V₁ and the point of engine failure. With turns this picture becomes more complicated as the engine failure procedure is based on V₂ while the engine failure may occur when the aircraft has already reached a speed of V₂ + 10 kt or more.

An extra complication is added when the engine failure occurs beyond the point where the SID routing deviates from the engine failure procedure.

Detailed obstacle clearance calculations cannot be performed for the state designed SID routings although sometimes the company does exclude specific SIDs from operation but then this will be, obstacle wise, very obvious.

Summarizing, when the engine failure occurs after clean-up or beyond the point where the SID routing deviates from the engine failure procedure, obstacle clearance is not assured.

Obstacle clearance calculations are made for worst case conditions only (conform the one engine out criteria) and are applicable to the track of the engine failure procedure as specified at the bottom of the TL table or, if no engine failure procedure has been specified, a track straight-out from the runway, and none other whatsoever.

Once a deviation from that track is made, it is the responsibility of the captain to establish a safe flight path, taking ATC requirements into consideration.

Therefore the captain should have a clear picture of the terrain and the options he will have obstacle wise.

A number of options exist:

• initiate a turn
• stop turning
• a climb in the existing configuration and at the existing speed
• level-off and clean-up
• continue following the SID
• a combination of the above.

Always inform ATC if a deviation from the cleared departure route is made.

Do not hesitate to declare an emergency if circumstances so demand (e.g. high workload due to ATC communication, difficulties in obtaining engine out flight path).

1.1.5 En Route Performance Requirements

01. General

When planning a flight, the requirements laid down in subpara 02 (one-engine-inoperative) shall be met.

Additionally, for 2-engine aircraft the maximum diversion distance from an adequate en route alternate shall not exceed 60 min. at single engine cruise speed in still air.

Exceedance of 60 min. maximum diversion distance may be granted subject certain conditions and prior authority approval.

The requirements laid down in subpara 03 (two-engine-inoperative) shall be met if a point along the intended track is more than 90 minutes at normal cruising speed away from a usable airport which fulfils the alternate landing distance requirements.

According to the US rules, the zone to be considered extends 4.34 NM to either side of the intended track. Company policy requires consideration of a significantly wider zone.

02. One Engine Inoperative

The one-engine-inoperative net en route flight path data should be determined by reducing the gross climb performance by a climb gradient of:

• 1.2% for twin-engined aircraft;
• 1.4% for three-engined aircraft;
• 1.6% for four-engined aircraft.

The configuration is as follows: the critical engine inoperative, the remaining engines operating at the available maximum continuous thrust and the airspeed as specified in the approved Airplane Flight Manual.

Compliance must be shown with either one of the following requirements:

Climb requirement

The net flight path must have a positive slope at:

• 1000 ft above all obstructions within the zone specified.
• 1500 ft above the airport where the aircraft is assumed to land after engine failure.

The weight of the airplane may be assumed to decrease in accordance with the fuel consumed.

Drift-down obstacle clearance requirement

After engine failure at the most critical point en route, the net flight path must allow the airplane to continue flight from cruise altitude to a usable airport, clearing all obstructions within the zone specified by at least 2000 ft. Furthermore a positive gradient of the net flight path is required at 1500 ft above the airport where the aircraft is assumed to land after engine failure.

The weight of the aircraft may be assumed to decrease in accordance with the fuel consumed. It is permissible to consider dumping of fuel provided at least 2 hours fuel reserve at the (new) destination is maintained.

Note: For stretches where en route requirements may be limiting, drift-down path or equivalents are published.

03. Two Engine Inoperative

The two-engine-inoperative net en route flight path should be determined by reducing the gross climb performance by a climb gradient of:

• 0.3% for three engined aircraft;
• 0.5% for four engined aircraft.

The configuration is as follows: two critical engines inoperative, the remaining engines operating at the available maximum continuous thrust and the airspeed as specified in the approved Airplane Flight Manual.

After simultaneous failure of two engines at the most critical point en route, the net flight path must allow the airplane to continue flight to a usable airport, clearing all obstructions within 5 NM on either side of the track by at least 2000 ft. Furthermore a positive gradient of the net flight path is required at 1500 ft above the airport where the aircraft is assumed to land after failure of two engines.

The weight of the aircraft may be assumed to decrease in accordance with the fuel consumed. It is permissible to consider fuel dumping provided a fuel reserve of at least 15 minutes cruise consumption is maintained at the airport where the aircraft is assumed to land after failure of two engines.

1.1.6 Landing Performance Requirements for Dispatch

01. Landing Runway Length

a. At destination

Basic requirements

The landing weight shall be such that it is possible to bring the aircraft to rest from a speed of not less than 1.3 V_S and from a height of 50 ft above the beginning of the landing runway length available:

1. assuming no wind, within 60% of the available length of the most favourable runway for landing in still air (normally this will be the longest runway), and
2. assuming the forecast wind conditions, within 60% of the available length of the most suitable runway for landing in view of forecast wind, landing aids, terrain, etc.

Operational factors

• elevation of the airport;
• 30% (150%) effect of forecast head (tail) wind component;
• expected consumption of fuel;
• if the runway is expected to be wet or slippery at arrival the available landing runway length must be factored by 100/115.

Note: Forecast temperature and runway gradient need not be taken into account.

Application

The maximum runway length limited landing weight is the lower of the weights resulting from requirements 1 and 2. Requirement 2 may be disregarded if an alternate is designated complying with the destination landing runway length requirements.

b. At alternate airports

The Basic Requirements and Operational Factors as outlined in a. also apply to “Alternate Airports”, except that it should be possible to bring the aircraft to rest within 70% of the available length of the runway for landing and that the available landing runway lengths need not be factored for wet or slippery surfaces.

Note: The company landing runway length required at alternates is equal to the “Dry destination” requirement for both DRY and WET runways at alternate.

Performance information

The relevant information in the Flight Manual is based on the following conditions and procedures:

• the aircraft shall be in the approved landing configuration. During the landing, changes in configuration, power or speed shall be in accordance with established procedures;
• the landing shall be preceded by a steady gliding approach down to the 50 ft height point with a speed not less than 1.3 V_S;
• the landing distance shall be based on a dry, hard surfaced runway;
• wheel braking so as not to produce excessive wear;
• other braking means also included, if safe and reliable (so far reverse thrust has not been permitted).

Note: In addition to dispatch landing runway length data the AOM contains actual landing distances to assist the pilot in exercising his judgement.

02. Approach Climb (One-Engine-Out)

In the normal approach configuration the steady gradient of climb shall not be less than:

• 2.3% for two-engined aircraft;
• 2.4% for three-engined aircraft;
• 2.7% for four-engined aircraft.

Operational factors when applying this requirement:

• forecast temperature;
• elevation of the airport;
• expected consumption of fuel.

Performance information is based on:

• critical engine inoperative;
• remaining engines at take-off thrust;
• speed as selected by the manufacturer, but not in excess of 1.5 V_S;
• flaps in approach position;
• gear up.

03. Landing Climb (All Engines Operating)

In the landing configuration the steady gradient of climb shall not be less than:

• 3.2% for all aircraft.

Operational factors when applying this requirement:

• forecast temperature;
• elevation of the airport;
• expected consumption of fuel.

Performance information is based on:

• all engines operating at the thrust which is available 8 seconds after initiation of movement of the power levers from the minimum flight idle to the take-off position;
• climb speed not in excess of 1.3 V_S;
• flaps in landing position;
• gear down.