Unstable approaches
Pay attention to these deadly sins to keep your landings safe.
By Shannon Forrest
ATP/CFII. Challenger 604, G-IV
Contributing Writer
The first step in solving any problem is admitting there’s a problem. Houston, we have a problem. Again.
Unstable approaches continue to be a leading cause of incidents, accidents, and violations. Aviation writers and safety pundits hate writing about this topic as much as pilots hate reading about it.
It’s more enjoyable to talk about the latest engine upgrades and entertainment systems rather than discussing accidents in which the probable cause was classified as failure to go around from an unstable approach. Yet here we are.
According to the FAA Safety Team (FAASTeam), a stable approach is defined as one in which the pilot establishes and maintains a constant angle glidepath toward a predetermined point on the landing runway.
It is based on the pilot’s judgment of certain visual clues, and depends on the maintenance of a constant final descent airspeed and configuration.
The Flight Safety Foundation’s approach and landing accident reduction tool kit goes on to point out that an approach is stable only if all the criteria in company standard operating procedures (SOPs) are met before or when reaching the applicable minimum stabilization in height.
Defining an unstable approach
When determining what constitutes a stable approach, there’s subtle variations among operators. However, the consensus seems to be that the aircraft should be within certain lateral and vertical parameters, within an upper and lower speed range, fully configured for landing at an acceptable descent rate, with all required briefings completed before reaching a point at a certain elevation above touchdown. Even with this knowledge, pilots continue to engage in behavior that culminates in unstable approaches.
An awareness of the 7 deadly sins of unstable approaches can aid in returning to safer operations. Failure to establish and document an SOP that defines a stable approach is sin number one. Although regulatory and safety agencies have proposed generic guidelines, each flight department and every aircraft operate slightly different. Therefore, it’s critical to define a stable approach as it applies to the specific operator.
Once parameters are defined, documenting them is essential. The process of defining and documenting provides a cogent and straightforward set of rules that instruct pilots when to execute the go-around.
A lack of rules promotes a psychological bargaining effect in which a pilot allows personal latitude to impact decision-making on the approach. For example, a pilot who unintentionally allows the speed to increase on final approach may be tempted to continue an approach rather than going around because he’s only going “a little bit faster than he usually flies, and the runway is long.”
This internal bargaining effect sets a potentially dangerous precedent because there’s no objective limit to defining an unstable approach. Today it was 5 kts over, but tomorrow it may be 15 or 20. No guidelines for when to go around also induces pilot skill level into the equation.
The “ace of the base” may be able to stop and make the first turn off from a high and fast approach, but a novice or new hire faced with the same situation could end up overrunning the runway. Written rules that apply to everyone make the go-around decision black and white rather than shades of gray.
Written rules are paramount
NTSB continually identifies lack of standards as causal in incidents and accidents. Smaller departments and owner operators tend to be the biggest violators of having no procedures manual. They believe that smaller or single-pilot operations don’t need written standards, but the opposite is true.
Written procedures as related to stable approaches enhance the pilot monitoring function by telling the pilot monitoring (PM) what to monitor. Failure to monitor – and correspondingly failure to intervene – is the second deadly sin.
On July 26, 2021, a Bombardier Challenger 605 operated under Part 91 crashed near TRK (Truckee CA) while attempting to circle to land to Runway 11 from an RNAV approach to Runway 20.
NTSB determined the probable cause to be “the first officer’s (FO’s) improper decision to attempt to salvage an unstable approach by executing a steep left turn to realign the airplane with the runway centerline, and the captain’s failure to intervene after recognizing the FO’s erroneous action, while both ignored stall protection system warnings, which resulted in a left-wing stall and impact with terrain.”
NTSB also noted that the deployment of flight spoilers to correct a high and fast condition 12 seconds before impact decreased the stall margin and contributed to the accident. Poor crew resource management (CRM), degraded decision making, and a self-induced pressure to perform were also cited as causal.
Ironically, the operator of the Challenger had a general operations manual (GOM) that defined a stabilized approach criteria as having the aircraft in a landing configuration and in a position for normal descent to the runway no later than 500 ft AGL in visual meteorological conditions (VMC) and 1000 ft AGL in instrument meteorological conditions (IMC). The GOM also called for the airspeed to be “on target” at such altitudes respectively.
According to the GOM, either pilot could call for a go-around, yet neither did despite the published stabilized approach criteria being violated. Under the PM paradigm, that’s the explicit job of the PM – call for a go-around when rules are violated. In this case, it appeared both pilots were attempting to salvage the approach individually rather than working collectively to return the aircraft to a safe condition.
Several times throughout the approach, the PM asked the pilot flying (PF) to relinquish control so he could fix the situation. Although it was not present in this situation, rank disparity can prevent the PM from speaking up and intervening when things go awry. A wide disparity in age, experience, background, and longevity within the flight department can be a barrier to inquiry, advocacy, and assertion – 3 tenets of CRM.
Automation plays a role
Under reliance on automation is sin number 3. You’re the PM nearing the end of a 4-hour flight late at night. Sleep last night was inadequate, catering never showed up, so you’re hungry and irritable, and just want the flight to be over.
The destination is a couple thousand feet above sea level, with an RNAV approach that depicts a higher-than-normal descent gradient to a down-sloping runway. The ceiling is 800 ft overcast. The combined effects of high density altitude, published gradients, and optical illusion of a down-sloping runway at night all indicate a higher probability of an unstable approach.
A couple of miles outside the final approach fix, the PF disconnects the autopilot and autothrottles, looks over, and says, “I’m going to hand fly this one.” The workload just exponentially multiplied on both the PF and the PM, further increasing the chances of an unstable approach.
Of course, you can’t talk about under reliance on automation without talking about over reliance on automation, and that’s sin number 4. Never hand flying and allowing the autopilot and auto throttles to manage the flight all the time is equally as bad. Pilots who never hand fly and then attempt to do so infrequently have a higher propensity for unstable approaches.
The answer to automation is the Goldilocks principle – not too much or too little, but just right. Automation is situationally dependent and should be used to increase the probability of stable approaches rather than intensify the possibility of a go-around.
Complying with ATC
Unwavering willingness to comply with air traffic control instructions comes in as the fifth deadly sin. Phrases like “maintain your best forward speed to the marker” or “make short approach” are common precursors to unstable approaches. A controller who withholds or issues a late descent clearance is also to blame.
Pilots seem to have a compulsion to comply, and doing so reinforces the controller’s errant behavior under the auspices that if nothing bad happens, the aircraft must be capable of doing it. If the aircraft doesn’t overrun the runway the controller has no way of knowing that the aircraft was outside of stable approach criteria in terms of speed or configuration.
Pressure to accept a visual approach in lieu of a published approach procedure with vertical guidance can also lead to premature descents that deviate from stable descent criteria. Until air traffic control hears the pilot utter the word “unable” and adjusts methodology accordingly, unstable approach prevalence will continue to be a problem.
Normalized deviance
Continuing an unstable approach knowing it violates defined parameters – whether pilot or ATC induced – is the sixth deadly sin. This is known as normalization of deviance.
Normalization of deviance – also called operational creep – is when the standard is violated so often that the violation inadvertently becomes the new standard. As a pilot becomes accustomed to continuing an unstable approach, he/she becomes habituated to it. For example, pilots are familiar with specific airports in which ATC tends to keep the aircraft high, followed by a rapid descent as a pilot gets vectored for the final approach fix. We even have a name for it – the slam dunk approach.
Many aircraft have difficult descending and reducing speed at the same time, especially when configuring for landing. Most times, these slam dunk approaches force a pilot to the order of things. For instance, sometimes the landing gear must be used as an ad hoc speed brake because the aircraft is too fast for deploying flaps. Pilots know these types of situations are technical deviances from standard, yet they’ve become “normal” and well known.
Intentional disobedience
The seventh and last deadly sin of unstable approaches is the most egregious: intentional non-compliance. This is when a pilot has a knowledge of the rules but makes a conscious and deliberate decision to violate them.
On May 5, 2021, a Gulfstream G150 overran the runway at 3J1 (Ridgeland SC). The crew requested a straight-in approach to Runway 36, even though the tail wind was estimated between 10–15 kts, and at times exceeded the manufacturer’s limitation.
During descent at 9000 ft the airspeed was maintained at 300 kts, despite the FAA rule that limits speed to 250 kts below 10,000 ft. The overspeed warning sounded multiple times. At 1.5 miles from the runway and at an altitude of 900 ft, the aircraft was not fully configured for landing and was 39 kts above ref speed.
The second in command (SIC) suggested S-turns to lose altitude and speed, but the pilot in command (PIC) responded, “Nah, we got it.” The descent rate increased so significantly that the GPWS warning system issued the “sink rate, sink rate, sink rate, pull up” aural alert. The
response from the PIC was, “we know it.”
The reason why the crew operated the aircraft outside of limitations and continued an unstable approach that resulted in an accident, was that they were racing another jet to the runway. It was common practice for one of the passengers to issue a challenge to the pilot to get to the destination as fast as possible. The crew willfully ignored rules and procedures to win a bet.
The solution
Identifying and avoiding unstable approaches requires a willingness to change. Pilots must start going around more frequently. This begins with normalizing the go-around both in terms of philosophy and training.
Go-arounds are uncomfortable in the sense that they don’t occur frequently. As a result, they are usually botched up to some degree. This can be solved by increased focus on the go-arounds during initial and recurrent training.
Lastly, pilots need to redefine mentally how they view the go-around.
A go-around is a success, not a failure. It’s avoiding the temptation of the 7 deadly sins and alleviating an undesired state that has far worse repercussions than just giving it another try.
Shannon Forrest is a current line pilot, CRM facilitator, and aviation safety consultant. He has more than 15,000 hrs TT and holds a degree in behavioral psychology.