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Article Information Category: Runway Excursion Content source: Flight Safety Foundation Content control: EUROCONTROL

Description

Most airlines and other aviation organisations specify minimum acceptable criteria for the continuation of an approach to land. These vary in detail but the following summary published by the Flight Safety Foundation is one view of the important considerations.

Their Approach-and-landing Accident Reduction (ALAR) Briefing Note 7-1 says that "all flights must be stabilised by 1000 feet above airport elevation in IMC and 500 feet above airport elevation in VMC. An approach is stabilised when all of the following criteria are met:

• The aircraft is on the correct flight path;

• Only small changes in heading/pitch are necessary to maintain the correct flight path;

• The airspeed is not more than VREF + 20 kts indicated speed and not less than VREF;

• The aircraft is in the correct landing configuration;

• Sink rate is no greater than 1000 feet/minute; if an approach requires a sink rate greater than 1000 feet/minute a special briefing should be conducted;

• Power setting is appropriate for the aircraft configuration and is not below the minimum power for the approach as defined by the operating manual;

• All briefings and checklists have been conducted;

• Specific types of approach are stabilized if they also fulfil the following:
  • ILS approaches must be flown within one dot of the glide-slope and localizer;
  • a Category II or III approach must be flown within the expanded localizer band;
  • during a circling approach wings should be level on final when the aircraft reaches 300 feet above airport elevation; and,

• Unique approach conditions or abnormal conditions requiring a deviation from the above elements of a stabilized approach require a special briefing.

An approach that becomes unstabilised below 1000 feet above airport elevation in IMC or 500 feet above airport elevation in VMC requires an immediate go-around."

Other applications of the Stabilised Approach principle frequently used outside North America do not distinguish between VMC and IMC approaches but instead specify aircraft status at a 'should' gate usually at 1000ft agl and then at a 'must' gate at 500ft agl. Failure to satisfy the former requires corrective action whereas failure to satisfy the latter requires a go around.

Effects

Continuation of an unstabilised approach to land may result in an aircraft arriving at the runway threshold too high, too fast, out of alignment with the runway centre-line, incorrectly configured or otherwise unprepared for landing. This can result in aircraft damage on touch-down, or runway excursion and consequent injury or damage to the aircraft or airfield installations.

Defences

The existence of an appropriate procedure which allows flight crew to determine whether an approach is sufficiently stabilsed to allow it to be continued at specified 'gates' with strict observance confirmed by automated tracking using the Operator's Flight Data Monitoring Programme.

Typical Scenarios

• An aircraft on approach to land is not stabilised after a late clearance to reduce speed. SOPs require the aircraft to go-around in the event of an unstabilised approach but the pilot continues the approach because of a desire to complete the flight on schedule, thus creating a signficant risk of consequential mishap affecting both the aircraft and its occupants.

Contributory Factors

• Adverse weather (e.g. strong or gusty winds, wind shear, turbulence).

• ATC pressure to maximise number of movements (e.g. high approach speed).

• Late change of runway.

• Commercial pressure to maintain schedule.

Solutions

• Strict enforcement of the stabilised approach principle by the company.

• ATC awareness of factors within their control which can contribute to an unstabilised approach.

Related Articles

• Loss of Control
• Accident and Serious Incident Reports: RE

Further Reading

DGAC (France) has published three documents in the English language related to non-stabilised approaches - click here

Flight Safety Foundation

• ALAR Briefing Note 7-1
• Copies of the FSF ALAR Toolkit may be ordered from the Flight Safety Foundation ALAR web-site http://www.flightsafety.org/current-safety-initiatives/approach-and-landing-accident-reduction-alar
• Reducing the Risk of Runway Excursions - Report of the Runway Safety Initiative
• Runway Excursion Risk Assessment Tool
• Non-stabilized Approach After ATC-Requested Runway Change (OGHFA SE)
• Runway Overrun On Landing (OGHFA SE)

Airbus Safety Library

• Airbus Approach Techniques Briefing Note - Flying Stabilized Approaches;

HindSight Articles:

• HindSight4 - Economy versus Safety - the Professional’s Dilemma;

Flight Data Services Case Study

• Case Study 6: Winglets and Low Power Approaches