Overweight landing

12/02/2010

Vereniging van Nederlandse Verkeersvliegers

Dutch Air Line Pilots Association

Position Paper 10 / 1 Overweight Landing

Revision: 4th February 2010

This position paper represents the opinion of the Dutch Air Line Pilots Association based on IFALPA / ECA policy, legislation, scientific research and manufacturer guidelines and recommendations.

Issue

An overweight landing is a landing made with a weight exceeding the maximum (design) structural landing weight. In case a situation requires an early return, pilots may consider an overweight landing or they may consider to burn off (or dump) fuel to reduce the gross weight to less than the structural limit. This position paper discusses in which circumstances pilots may elect to land overweight and what to consider in case an overweight landing will be performed.

Design Criteria

Structural – Impact Resistance

Aircraft manufacturers have to meet design criteria for the impact resistance capability of the aircraft structure. These design criteria are laid down in the EASA Certification Specifications CS-25 and the FAA Federal Aviation Regulations (FAR) Part 25. Meeting requirement CS/FAR 25.723 and CS/FAR 25.473, the energy an aircraft structure can absorb is proven to be sufficient even at a 6 fps touchdown at the design takeoff weight. (1) (2) Typical sink rates at touchdown are in the order of 2 to 3 feet per second and even a hard landing rarely exceeds 6 feet per second. But neither FAR nor CS-25 requires a manufacturer to consider asymmetrical loads on the undercarriage involved in a crosswind landing impact. Therefore, since higher weights in a crosswind situation imply higher assymetrical loads on the undercarriage, making a crosswind landing at higher weights increase the risk of damaging the undercarriage. Neither does staying within the demonstrated crosswind limit guarantee a safe landing, since this “limit” is demonstrated by well-trained, well-rested pilots landing the aircraft on a dry runway with a weight not exceeding the maximum structural landing weight.

Structural –Brake Energy

The minimum required Kinetic Energy Capacity of the wheel brakes must be based on the critical landing weight where, according FAA AC 25.735-1 and AMC 25.735, the critical landing weight for this condition is the maximum takeoff weight. Normally, landing brake energy is not a problem for an overweight landing because the brakes are sized to handle a rejected takeoff at maximum takeoff weight.

Performance – Landing Distance

The maximum landing weight is limited by landing field length requirements and go-around climb gradient requirements. This means that the landing weight much be such that the aircraft can either come to a full stop safely or make a safe go-around. Regarding the landing distance it is obvious that a higher landing weight requires a longer landing distance available to deplete the present kinetic energy and bring the aircraft to a full stop. Dispatch landing distance calculations are there to limit the planned weight with such a margin that a pilot normally not have to make critical landing performance decisions inflight. This confidence can lead to not making landing calculations regarding required landing distance. In most (unchanged) landing situations this will not cause any trouble but in the overweight landing case this can imply a significant risk of a landing overrun, especially when the pilot is trying to make a soft landing by holding off the aircraft, thereby increasing the air distance (distance from threshold to touchdown) significantly.

Performance – Go Around

With respect to the go-around, CS/FAR 25.119 and 25.121 require minimum achievable go-around climb gradients in an all-engines-operating as well as an engine failure situation. When these requirements cannot be met at maximum takeoff weight, CS/FAR 25.1001 requires installation of a fuel-jettison system. Aircraft not equipped with a fuel-jettison system will therefore meet the regulatory go-around climb requirements at maximum takeoff weight. This however does not guarantee achievement of a higher than the regulatory climb gradient due to high terrain in the go-around flight path (e.g. INN).

Operations

Emergency Situation

According to CS/FAR 25.1519 the airplane weight must be established as an operating limitation and FAR 91.9 does not allow a pilot to operate a civil aircraft without complying with the operating limitations. However, in case of an emergency that requires immediate decision, FAR 121.557/559 and OPS 1.085 allow the pilot-in-command to deviate from rules, operational procedures and methods and to take any action that he/she considers necessary under the circumstances in the interest of safety. These rules therefore allow an overweight landing but preclude such if there is no emergency situation. AMC 25.1581 describes an emergency as “a procedure requiring immediate flight crew action to protect the aeroplane and occupants from serious harm”. Since OPS 1.607 mentions that the maximum structural landing mass is the maximum permissible total aeroplane mass upon landing under normal circumstances, an overweight landing is clearly not considered a normal situation. Moreover, in Appendix 1 to OPS 1.1045 (Operations Manual contents) the overweight landing situation is also listed under abnormal and emergency procedures requiring special additional procedures.

Other Considerations

When making an overweight landing, crew have to consider the following as well:

  • Overweight autolands are not recommended by the manufacturer.
  • A higher landing weight requires a higher approach speed, which decreases the margin to flap limit speed. Therefore the risk of a flap load relief is increased, especially with high winds and/or gusts. The desired windcorrection may therefore be limited. A flap load relief may lead to landing with a lower flapsetting, which increases the required landing distance.
  • Using a lower than standard landing flapsetting, increases the risk of exceeding the brake energy limits, affecting the aircraft’s stopping capability.

Allowable Circumstances

Air Carrier Operations Bulletin 72-11 (1972) mentions three examples of situations the FAA considered typical of those under which pilots may be expected to use their emergency authority in electing to land overweight:

  • Any malfunction that would render the airplane unairworthy.
  • Any condition or combination, thereof, mechanical or otherwise, in which an expeditious landing would reduce the exposure to the potential of additional problems which would result in a derogation or compromise of safety.
  • Serious illness of crew or passengers which would require immediate medical attention.

In a situation where an overweight landing will be made, there may be guidelines in the aircraft Training manual (e.g. Boeing’s Flight Crew Training Manual).

Conclusions

  • Aircraft are designed to safely resist a hard landing with maximum takeoff weight and without exceeding the brake energy limits on a landing without crosswind. But when a crosswind landing is made there is no guarantee that the undercarriage will not be damaged due to excessive assymetrical loads even within the maximum demonstrated crosswind limit.
  • An overweight landing increases the risk of a landing overrun especially when trying to make a soft landing. It also decreases the margins to flap limit speeds during the approach and brake energy limits during the rollout.
  • If an aircraft is not equipped with a fuel jettison system, the minimum required go-around gradients (a higher than minimum required gradient due to terrain is not considered) can be met with maximum takeoff weight. Regarding aircraft equipped with a fuel jettison system this is not guaranteed.
  • Both EASA and FAA consider MLW an operating limitation but allow the PIC to deviate from this in case of an emergency.
  • EASA considers an overweight landing at least as abnormal, requiring additional procedures.
  • Making an overweight landing for economical / environmental reasons is not mentioned as an allowable situation to make an overweight landing.

References

  1. FAA/EASA Certification Specifications 25.119
  2. FAA/EASA Certification Specifications 25.121(d)
  3. FAA/EASA Certification Specifications 25.473(a)(2)&(3)
  4. FAA/EASA Certification Specifications 25.723(a)(1)
  5. FAA/EASA Certification Specifications 25.1001(a)
  6. FAA/EASA Certification Specifications 25.1519
  7. EU OPS 1.085(g)
  8. EU OPS 1.607(c)
  9. FAA Code of Federal Regulations (FAR) 91.9(a)
  10. FAA Code of Federal Regulations (FAR) 121.557
  11. FAA Code of Federal Regulations (FAR) 121.559(a)
  12. EASA Acceptable Means of Compliance 25.735
  13. EASA Acceptable Means of Compliance 25.1581(3)(f)
  14. Appendix 1 to EU OPS 1.1045(B)(3)(3.1)(d)
  15. FAA Advisory Circular 25.735-1
  16. Air Carrier Operations Bulletin 72-11
  17. Boeing Aero Magazine QTR 3.07