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|Category:||Emergency & Contingency|
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Emergency Turn refers to the path over the ground that is followed by an aircraft that has experienced an engine failure during takeoff. An Emergency Turn is interchangeably referred to as an Escape Routing or as an Engine Out SID.
Takeoff and initial climb performance requirements following an engine failure are specified in National Regulations. These regulations require that the aircraft be capable of meeting a specified minimum climb gradient, the value of which is dependent upon the number of engines installed and the regulatory criteria under which the aircraft has been certified, until reaching 1500' AGL or the minimum enroute altitude.
Takeoff performance can be limited by any of the following:
- runway characteristics including Take Off Distance Available (TODA), Accelerate Stop Distance Available (ASDA), elevation, slope and the presence of contamination
- atmospheric conditions including temperature, wind and pressure
- aircraft limitations including maximum takeoff weight, maximum tire rotation speed, maximum allowable time at takeoff thrust and any performance decrements due to Minimum Equipment List (MEL) or Configuration Deviation List criteria
- certification criteria for engine out climb performance
Under the regulations, the Maximum Takeoff Weight (MTOW) can be limited by certification criteria that require a gross engine out climb gradient of 2.4%, 2.7% or 3.0% for two, three and four engine aircraft respectively. To ensure obstacle clearance while allowing for aircraft performance degradation and less than optimum pilot technique, the gross gradients are reduced by 0.8%, 0.9% and 1.0% respectively to calculate a net gradient. This net gradient is then published in the Aircraft Flight Manual (AFM) performance data and, in actual operations, must ensure that the limiting obstacle in the departure path is cleared by a minimum of 35'. If there is an obstacle within the departure path that cannot be avoided and would not be cleared by 35', the planned takeoff weight must be reduced until minimum obstacle clearance can be achieved. Note that turns during the intial climb are limited to 15° of bank and that turning will result in a reduction in aircraft climb capability.
Standard Instrument Departures (SID)
Standard Instrument Departure (SID) routings are designed to allow efficient traffic flow, avoidance of noise sensitive areas and deconfliction from both arrival traffic and the traffic from other aerodromes. They also ensure obstacle clearance provided that the standard minimum climb gradient of 200'/nm (3.3%) or, when published, a specified higher climb gradient is met. The standard 3.3% SID gradient exceeds the certification requirements for engine out climb capability in virtually all transport category aircraft. Consequently, in the engine failure case, following the SID routing does not necessarily ensure obstacle clearance.
Emergency Turn Development
AFM charts allow calculation of the MTOW that meets the minimum regulatory climb gradient. These charts take into consideration the runway characteristics of slope and contamination and the prevailing atmospheric conditions of wind, temperature and pressure altitude. However, unless the departure path is also assessed for obstacles, obstacle clearance and safety of flight is not assured. Obstacles may be natural, such as hills or trees, or man-made, such as buildings, towers, light standards and power lines. If an obstacle penetrates the obstacle identification surface of the required regulatory gradient, the departure aircraft must either turn to avoid it or the gradient must be increased to provide the minimum required obstacle clearance. In either case, a reduction of MTOW will be necessary. Note that it is possible that Emergency Turn and SID routings will partially or completely overlap.
It is a commercial imperative to maximize payload capability without compromising safety. Emergency Turns are intended to achieve that goal. Whenever possible, escape routings will avoid turning as turns result in a loss of climb capability and necessitate a reduction in weight. If turns are required, turns below 1000' AGL will be avoided unless there is no other alternative. If a low turn is required, the minimum height above ground for turn initiation is the greater of 50' or one half of the wing span of the aircraft. The maximum allowable bank angle below 400' AGL is 15 degrees. Procedures must also be designed to ensure that the 3rd climb segment (level acceleration / flap retraction) can be safely completed and thrust/power reduced to maximum continuous prior to the regulated time limit for takeoff thrust.
Some airlines have performance engineers on staff to conduct runway analysis and produce Emergency Turn data for their company. Other Companies utilize third-party providers to generate the required information. In both cases, for any specific runway, crews will be provided with an escape routing, a minimum acceleration altitude and the means to calculate the MTOW. Calculations will take the existing atmospheric conditions and any runway contamination into consideration. The calculation medium might be paper charts or an Electronic Flight Bag(EFB) for crew use or a TLR (Takeoff / Landing Report) generated by the dispatcher.
Flight Crew Actions
In the event of an engine failure after takeoff, crews must be prepared to immediately deviate from any cleared routing that is inconsistent with the Emergency Turn routing while concurrently carrying out the specified engine failure after takeoff (EFATO) drills. Both elements are critical to a successful outcome as the engine out drills ensure aircraft control and optimum climb performance while adherence to the Emergency Turn routing provides for obstacle clearance. Failure to comply with either element could result in disaster.
In the event of a deviation from the cleared routing, flight crew should advise ATC of the deviation as soon as practicable incorporating the term “STANDBY” at the end of the message to limit the distraction of subsequent ATC calls until the flight deck situation is under control.
Suggested Controller’s Actions
Best practice embedded in the ASSIST principle could be followed (A - Acknowledge, S - Separate, S - Silence, I - Inform, S - Support, T - Time) :
- A - acknowledge the emergency and ask for the crew's intentions when their situation permits. Respect the “STANDBY” transmission and wait for the flight crew to indicate when they are able to provide further information
- S - separate conflicting traffic from the emergency aircraft. This is particularly critical when an emergency turn requires the aircraft to deviate from its cleared routing. Prioritise it for landing and, when appropriate, keep the active runway clear of departures, arrivals and vehicles
- S - silence the non-urgent calls (as required) and use separate frequency where possible
- I - inform the airport emergency services and all concerned parties according to local procedures
- S - support the flight experiencing the engine failure with any information requested or deemed necessary (e.g. type of approach, runway length and aerodrome details, etc.)
- T - provide time for the crew to assess the situation, don’t press with non-urgent matters
The controller should be prepared to:
- Acknowledge emergency on RTF
- Take all necessary action to safeguard all aircraft concerned
- Suggest a heading, if so required or requested
- Provide separation or issue essential traffic information, as appropriate
- Emergency broadcast if necessary
- When the flight crew indicate they can accommodate further R/T communication, ask for pilot’s intentions and other important information, such as:
- Aircraft damage
- Fuel remaining
- Total passengers and crew
- Uncontained Engine Failure
- Engine Failure During Takeoff - Multi-Engine Transport Category Jet Aircraft
- Net Take-off Flight Path
- Engine Failure: Guidance for Controllers
- Rejected Take Off
- SIDs and STARs
UK CAA - Safety Regulation Group
Airbus Flight Operations Briefing Notes
- Handling Engine Malfunctions
- Revisiting the “Stop or Go” Decision
- Understanding Takeoff Speeds
- Getting to Grips with Aircraft Performance pages 63 and 64.
US Federal Aviation Administration