Non-stabilized Approach After ATC-Requested Runway Change (OGHFA SE)
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|Content source:||Flight Safety Foundation|
|Human Factors Aspects||Risk Assessment, Unexpected Events, Crew Resource Management, Press-on-itis|
|ENR / APR|
|Operator's Guide to Human Factors in Aviation|
|Non-stabilized Approach After ATC-Requested Runway Change|
The Accident as a Situational example
The twin-engine airplane is high and fast on approach to runway 08, having prepared for runway 33 with a briefing from the captain, who is pilot flying (PF). You, as first officer, obtained automatic terminal information service (ATIS) information during the descent that indicated strong westerly winds on the ground. Because of high terrain, the most common approach to runway 33 is via the Instrument Landing System (ILS) approach to runway 08 with a circle-to-land maneuver southwest of the airport for a landing on runway 33.
ATC advises you the ATIS has been updated and you should expect a straight-in approach to runway 08, the most common approach and familiar to you. You have slightly more than 5 min to prepare for landing on the new runway from notification to approach clearance. Without performing a completely new approach briefing, you prepare for this change by confirming your previously planned flap setting of 40 degrees, calculating a target airspeed of 138 kt.
As the aircraft is flying assigned headings and descending steadily with the autopilot engaged, crew workload initially was relatively low. The short time available to prepare the approach is now almost entirely consumed by routine communications with ATC.
Runway 08 is relatively short, adequate for landing but providing little margin for error. While you are obtaining the new ATIS, the captain receives and acknowledges ATC instructions to maintain 230 kt or more until advised, with vectors to a base leg to intercept the final approach path.
When the aircraft receives clearance for a visual approach to runway 08, it is at some 230 kt, at 4,200 ft msl, approximately north of the extended runway centerline and almost 10 mi west of the runway. Airport elevation is approximately 800 ft msl, meaning that the airplane has to slow 95 kt and descend some 3,400 ft to reach a runway about 10 mi away by the planned ground track.
Do you continue to proceed with the approach?
Positioned too high, too fast and too close by ATC, you are faced with the difficult if not impossible task of establishing a stabilized approach, given the characteristics of the airplane. The other option is to extend the approach path in cooperation with ATC or even to go around despite the traffic.
One minute after being cleared for approach, autopilot is engaged with manually-commanded idle thrust; the first configuration change is performed to get the aircraft below 225 kt, the maximum speed to extend flaps to 5 degrees. In quick succession the captain then commands extension of the landing gear and the flaps, in stages, to 40 degrees.
The aircraft crosses abeam the waypoint navigation aid, descending to 3,000 ft, slowing through 225 kt and slightly overshooting the final approach course on autopilot.
What would your landing strategy be?
The captain then disconnects the autopilot and brings the aircraft back on course, ordering the gear to be extended and successive flap extensions, maintaining 3,000 ft until 3 mi from the threshold. Flaps 40 is commanded while the aircraft is above 180 kt. Placard speed for this setting is well below this speed and is never achieved.
The aircraft then slows to 180 kt, and the captain is flying it at more than twice the normal 3-degree gradient in his efforts to touch down just beyond runway threshold.
When the aircraft passes below 1,200 ft above ground level and its descent rate increases through 2,900 ft/min, the ground-proximity warning system (GPWS) “sink rate” warning starts to sound continuously, later followed by the more stringent “whoop, whoop, pull up” warning.
What is your reaction?
However, when the aircraft reaches 1,000 ft above airport elevation, its airspeed has increased to almost 200 kt with a 14-kt tailwind, and it is descending at more than 2,600 ft/min. When descending through 500 ft, 16 sec from touchdown, speed is unchanged and descent rate is almost 2,000 ft/min. You miss the 500-ft callout as you are also concerned about the aircraft that has landed ahead and has not yet cleared the runway. Despite all this, the aircraft continues at a steep gradient of 7 degrees until the captain begins the flare for landing at approximately 150 ft above ground level.
Although he manages to land the aircraft within the normal touchdown zone, he has not been able to slow the aircraft while descending at that angle. Despite the engines remaining at idle, the aircraft is flying on average some 45 kt faster than the target speed throughout the final approach and landing. The aircraft touches down at a speed of 182 kt with a 6-kt tailwind, some 2,150 ft beyond the runway threshold with approximately 3,900 ft of runway left and approximately 4,150 ft remaining to the blast fence at the far end of the runway. The captain apparently does not apply and hold maximum brake pressure. It is the airline’s policy to use manual braking rather than autobraking during landing rollouts. One advantage of the airplane’s autobraking system is the faster application of heavy braking following which a crew can take over with maximum manual braking for even faster deceleration. The captain applies braking “pretty well” and uses reverse thrust.
However he is unable to stop, so he steers to the right near the end of the runway, but the aircraft continues and passes through the airport boundary and across a street, stopping near a gas station. Two passengers are seriously injured, while the captain and dozens of passengers receive minor injuries leaving the seriously damaged airplane.
Data, Discussion and Human Factors
Approach-and-landing accidents account for 55 percent of hull losses and 50 percent of fatalities. (Flight Safety Digest, “Killers in Aviation,” 1999.) It was fortunate that this accident did not result in loss of life.
The accident report stated that the probable cause of the event was the pilots’ excessive speed and steep flight path angle during approach and landing and their failure to abort the maneuver when stabilized approach criteria were not met. It conceded that ATC contributed to the accident by imposing a runway change and positioning the aircraft for a too-steep, or “slam-dunk,” approach with no other alternative than a go-around.
However, discussing the event in human factors terms provides more subtle clues as to what might have precipitated this flight into an almost irreversible chain of events. It includes some latent issues within the training organization. Most airline training focuses on specific maneuvers and not enough on exercising judgment in realistic scenarios that feed back on behavioral and even technical issues.
In this case the respective issues were:
- How to refrain from a high and fast approach;
- How to descend properly without haste; and
- How to stop an airplane after touchdown using auto-braking and reverse thrust, with manual braking later.
The following points bring to light the human factors elements in this particular case:
- Changing surface wind conditions at the destination airport required the crew to change the arrival plan.
- Any runway change during descent also carries implied or explicit pressure to accept ATC instructions without much time to consider the new assignment.
- Reflecting industry concerns with on-time performance and fuel efficiency and unaware of the risks associated with rushed approaches, the crew went into press-on-itis mode and demonstrated its flexibility to integrate into traffic and keep operations fluid.
- A contributing factor may have been the familiarity with runway 08 instead of the more challenging approach to runway 33 with a circle-to-land near terrain that was canceled by ATC. Time was short, so the pilots did not consult the onboard performance computer. Although this would have indicated that the landing was possible, it could have alerted them to various implications for the new approach.
- ATC caused the flight to be both fast and high when beginning the approach.
- Between the time they were informed of the new runway assignment and the time they got the approach clearance — some 5 min — the crew, experienced on the type, knew that they would face a high and fast situation.
- ATC vectored the aircraft on a heading to base leg to the final approach course at 230 kt, which placed it at its outer limits for descent and slowdown in the remaining distance to touchdown. It was a not uncommon “slam-dunk” clearance that challenged the crew to get stabilized in speed, descent rate and glideslope before landing.
- Neither pilot expressed concerns about the ATC instructions nor did they communicate their thoughts about descent planning. The increased workload may have interfered with their perception and situational awareness of the risks involved. When facing high workloads, crews can fall into a reactive thinking process that reduces cognitive demands and strategic risk and situation assessment.
- The captain attempted to descend to the runway without making the maximum effort to slow the aircraft.
- Slightly more than one minute passed between the clearance to approach visually and the first configuration change. From then on, the captain’s situational awareness that the aircraft was high and fast was confirmed by the quick succession of actions to configure the aircraft for landing.
- These actions also suggest that he did not recognize how important it was to slow down in the air as much as possible before attempting to stop the aircraft on the runway. The most efficient way to accomplish this is to level off, extend the gear, slow down and configure all the way to flaps 40 degrees, then resume descent.
- Also contributing to the captain’s decision to descend before slowing down was the fact that he was rather surprised at being closer to the airport than he actually thought after passing the waypoint navigational aid. The attention of both pilots may have focused on the threatening perspective of runway 08, which appeared foreshortened, steep and well beyond any normal approach. It created tunnel vision under heavy workload and stress, possibly disrupting judgment and depleting resources for critical thinking and decision making.
- There is a normal tendency among pilots to begin descending when the airplane display indicates the aircraft is high on approach. This quickly makes the display appear normal. When this occurs, knowledge of the total energy concept and discipline help pilots to choose slowing before descending, though this makes the display initially appear worse. Dissipating total energy can only happen by increasing drag (gear extension before flaps) or extending distance to landing; descending more rapidly does not lead to a total energy decrease.
- Despite excessive airspeed, the pilots continued with their plan to land and did not execute a go-around:
- The steep descent gradient, the abnormally high airspeed, the excessive descent rate and the idle throttle setting did not trigger any reverse reaction. Neither did cues such as the GPWS “sink rate“ and “pull up” warnings.
- These continuous auditory warnings throughout the final seconds before landing were a possible distraction. Just before the flare, the crew had apparently also been subject to extra distraction due to concerns that the aircraft ahead had not cleared the runway, largely because of the excessive final approach speed. Warning systems, although designed for accident prevention, can often have an unintended interference effect.
- The airline also provided specific guidelines with precise stabilized approach gates that call for proper pilot not flying (PNF) monitoring, specific callouts and go-around/missed approach criteria. Most approaches involve some degree of leeway to deviate within realistic tolerances before discontinuing the approach, which facilitates the crew decision-making tasks. This may in particular strengthen the resolve of first officers when having to challenge their captains. It also creates the necessary bonding to guide a captain’s decisions. The absence of verbal challenges from the first officer through callouts on excessive airspeed, off-scale glide-slope deviation, excessive sink rates, improper flap speed configuration or standard altitudes confirms poor crew resource management (CRM), required to keep the PF abreast of what’s happening and getting feedback on his situational awareness.
- The first officer only reconfirmed the landing clearance 40 sec after clearance to land on runway 08 was issued and executed the landing checklist silently. He was too busy to verbalize it, dropped less crucial tasks to cope with excessive workload and lack of time, which impaired proper safety assessments.
- This vulnerability led to overconfidence bias — a tendency to overestimate one’s own abilities — and to confirmation bias — a tendency to hold on to a preconceived plan and to seek elements confirming it. It meant the pilots were reluctant to abandon the approach, felt committed after heavy investments in time and effort and facing contradictory cues despite ample evidence against carrying on.
- The captain delayed application of maximum braking.
- The crew’s delayed situational awareness is confirmed by the fact that even after touchdown it was not readily apparent to them from the available cues that they were in a critical situation that needed utmost care.
- Upon touchdown, the captain did not immediately apply and hold maximum brake pressure and reverse thrust.
- Even if auto braking had been used, the aircraft would not have stopped in time, but stopping performance would have been better. The pilots could have selected maximum manual braking as soon as they became aware of the threat ahead and would have been able to decelerate even faster.
Prevention Strategies and Lines of Defense
Some airports have instances of slam-dunk events that illustrate the importance of prevention and countermeasures.
Among the salient protections should be when there is a change in operating runway and insufficient time available to prepare the approach, a crew must focus more on being prepared for a go-around.
The following strategies are recommended in order to avoid this type of incident:
- Perform accurate risk assessments and tactical decision making based on
- Weather and winds
- Approach type
- Risk of specific threats such as workload, a slam-dunk approach and being too high, too fast and too close
- Conduct effective briefings that fully review the approach procedures, profile and aircraft configurations, including specific approach callouts
- Explicitly define task sharing with clear monitoring of critical flight parameters such as airspeed, glideslope, sink rate, flap-speed configuration and altitudes
- Explicitly agree on approach criteria limits beyond which a go-around or other recovery action will begin
- Maintain critical thinking and decision making to avoid disrupting judgment
- Avoid press-on-itis and stress by not yielding to ATC or time pressures to rush as you may fall prone to other human factors such as overconfidence, confirmation bias or tunnel vision
- Maintain communications and buy time to create common situational awareness among crewmembers
Applicable principles lead to simple guidelines that can avoid trouble if applied correctly:
- Communicate with each other through briefings, callouts, concerns and risk assessments to make sure that the entire team is on the same wavelength
- Do not fixate on completing the landing at first attempt
- Cross check what you see, hear and feel with available flight instruments
- Keep discipline by applying proper descent and braking techniques after landing (SOPs), by attending to warnings such as GPWS “sink rate” and “pull up”
- Maintain proficiency through training to exercise CRM, airmanship and judgment
This Situational Example describes an approach accident caused by a slam-dunk approach induced by ATC that was ignored by the crew because of its desire to push on. Understanding the particular reasons why this crew encountered problems can help realize the intricacies of being dragged into an non-stabilized approach, which is more common than one would realize. This accident was preventable if the flight crew had recognized they were driven by ATC into a high and fast situation which they could and should have refused.
Addressing human factors issues in the operational situation of an non-stabilized approach after an ATC-requested runway change revealed the following:
- Insufficient time was taken to prepare for the essential aspects of an approach
- Basic principles for slowing down — leveling off, extending the gear and configuring — before descending were omitted in preference for adapting to the display configuration by immediately increasing the descent rate and hence speed and glideslope angle
- Tunnel vision under heavy workload and stress crept in, thereby disrupting judgment, critical thinking and decision making
- Situational awareness was lost because of the quick succession of individual and crew-coordinated actions to try to make it to a safe landing
- Teamwork to share, review and implement appropriate decisions was fragmented at the expense of PNF monitoring, respecting go-around/missed approach criteria, specific callouts, challenge response checklists, stopping performance
- Pressures, stress and distractions due to unexpected events were no longer managed
Additional OGHFA Material
- Situational Awareness
- Flight Preparation and Conducting Effective Briefings
- Stress and Stress Management
- Decision Making
- Decision Making Training
Additional Reading Material
- Flight Safety Foundation Approach and Landing Accident Reduction (ALAR) Toolkit
- FSF Flight Safety Digest, “Stabilized Approach and Flare are Keys to Avoiding Hard Landing,” August 2004. Note: this document is not currently available from the FSF website.