Stabilised Approach
Stabilised Approach
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 suggests 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 + 20kts 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 used outside North America do not necessarily distinguish between VMC and IMC approaches, which makes it possible to track compliance using OFDM.
Some Operators also specify aircraft status at a "should" gate ahead of the "must" gate envisaged by the FSF system. This is typically 500 feet above the 'must' gate, for example a 'should' gate at 1000ft AGL followed by a "must" gate at 500ft AGL. Failure to satisfy the former requires that corrective action is feasible and taken 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 stabilised to allow it to be continued at specified 'gates' with strict observance confirmed by automated tracking using the Operator's Flight Data Monitoring (FDM) Programme. Note that if the Flight Safety Foundation recommendation that there should be different 'gates' for IMC and VMC is followed, then such tracking becomes impossible.
Example Scenario
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 compliance with the stabilised approach principle by pilots.
- ATC awareness of factors within their control which can contribute to an unstabilised approach.
Accidents and Incidents Involving Unstabilised Approaches
On 12 March 2022, an ATR76-600 Captain made an unstabilised approach to Jabalpur before a first bounce more than half way along the runway and a final touchdown 400 metres from the runway end. The First Officer took control but did not commence a go-around and the aircraft overran the runway before stopping. The Captain had just over four months command experience and had made six similar ‘high-severity long-flare’ approaches in the previous five days but these had gone undetected because although such exceedances were supposedly being tracked by company flight data monitoring, this event was not being tracked.
On 11 February 2022 an Airbus A320 making a visual approach to Guadeloupe at night was advised by ATC of a descent below the minimum safe altitude after continuing the approach after visual reference was temporarily lost. A repeat of this warning by ATC prompted crew recognition that the aircraft was not on the required approach track or profile and a go around was initiated from 460 feet agl. The decision to attempt a visual approach in unsuitable circumstances and a delay in recognising the need for a go-around were found to have been symptomatic of poor tactical decision making.
On 31 January 2022, a Bombardier Challenger 604 pilot lost control during the final stages of a London Stansted night crosswind landing. A bounced nose-gear-first touchdown was followed by a brief runway excursion onto grass before a return to the runway and a climb away. A diversion to London Gatwick followed without further event but subsequent inspection revealed structural and other damage sufficient to result in the aircraft being declared an economic hull loss. The Stansted touchdown was found to have occurred after a premature flare at idle thrust continued towards the stall and a momentary stick pusher activation occurred.
On 27 January 2020, an MD83 made an unstabilised tailwind non-precision approach to Mahshahr with a consistently excessive rate of descent and corresponding EGPWS Warnings followed by a very late nose-gear-first touchdown. It then overran the runway end, continued through the airport perimeter fence and crossed over a ditch before coming to a stop partly blocking a busy main road. The aircraft sustained substantial damage and was subsequently declared a hull loss but all occupants completed an emergency evacuation uninjured. The accident was attributed to the actions of the Captain which included not following multiple standard operating procedures.
On 28 April 2018, a Dassault Falcon F900B came into close proximity with a Beech B36T Bonanza at the uncontrolled VFR-only aerodrome at Bremgarten during its tailwind approach to runway 23 made without contacting the designated Flight Information frequency as the other aircraft was on approach to runway-in-use 05 and in contact with Flight Information. The Beech pilot took avoiding action by turning north and climbing in order to avoid a collision. The Falcon 900 crew had not prepared for the approach which was then unstabilised with late gear extension and multiple EGPWS ‘SINK RATE’ warnings annunciated.
SKYclips
Related Articles
- Approach and Landing Accidents (ALA)
- Loss of Control
- Go Around
- Accident and Serious Incident Reports: RE
- Non-stabilized Approach After ATC-Requested Runway Change (OGHFA SE)
- Runway Overrun On Landing (OGHFA SE)
- Global Action Plan for the Prevention of Runway Excursions (GAPPRE)
Further Reading
- Go-Around Safety Forum, Brussels 2013: Findings and Conclusions
- Global Action Plan for the Prevention of Runway Excursions, Part 1 Recommendations and Part 2 Guidance and Explanatory Material, EUROCONTROL/Flight Safety Foundation, 5 May 2021.
DGAC (France) has published three documents in the English language related to non-stabilised approaches.
Flight Safety Foundation
- ALAR Briefing Note 7.1 - Stabilized Approach
- ALAR Briefing Note 8.1 - Runway Excursions and Overruns
- Reducing the Risk of Runway Excursions - Report of the Runway Safety Initiative
- Runway Excursion Risk Awareness Tool
- Copies of the FSF ALAR Toolkit on CD may be obtained from the Flight Safety Foundation
Airbus Safety Library
- Airbus Approach Techniques Briefing Note - Flying Stabilized Approaches
- Control your Speed… During Descent, Approach and Landing, Airbus Safety First Magazine, #24, July 2017
CANSO
- Runway Excursions - An ATC Perspective on Unstable Approaches
- Avoiding Unstable Approaches - Important Tips for ATCOs
- Unstable Approaches – ATC Considerations, January 2011
HindSight Articles:
Flight Data Services Case Study
