One unstable approach too many
28 March 2014
Posted by: Brian MacDonald
According to international air industry figures, 3.5 to 4 percent of all aircraft approaches to landing are unstable; and of those, 97 percent actually continue to a landing. Most of the time, everything works out just fine. But sometimes there are consequences: a runway overrun, a tail strike, or in the case of Resolute Bay, Nunavut, on August 20, 2011, a fatal crash. It’s time to put a spotlight on this issue to see what needs to be done to address this ongoing problem.
Any pilot will tell you that landing is one of the most critical phases of flight, in part because the aircraft is maneuvering at a much slower speed, and much closer to the ground. A stabilized approach helps to ensure that the plane is ready for landing and that the pilots are prepared for the demanding task of landing an aircraft.
Many air transport operators incorporate stabilized approach policies and procedures within their operations. This is intended to be an administrative defense against several negative outcomes, such as runway overruns and controlled flight into terrain (CFIT).
A stable approach involves controlling, and stabilizing, several key criteria before the aircraft reaches a predefined point – usually several miles back from the airport, at 1000 feet above the ground. These criteria include:
- Course – The aircraft is on the prescribed track to land. This avoids any excessive bank angles during the final moments before landing;
- Speed – Should be within a few nautical miles per hour of appropriate speed for approach conditions of weight and weather. This provides the slowest speed for landing, but with built in safety margins;
- Rate of descent – Should be set to maintain the glide path. This avoids excessive changes and allows an optimum closure rate to the runway surface,
- Power setting – Should be set to maintain optimum airspeed and rate of descent previously mentioned. This prevents excessive changes to airspeed and rate of descent and ensures the engines are in a power range that allows for rapid acceleration should a go-around be required; and
- Aircraft configuration – The landing gear should be down and final flap selection completed. This avoids configuration changes in the final moments of the approach which could in turn adversely affect speed, rate of descent and power setting
An approach is considered stabilized if all criteria in company procedures are met before or when reaching the predefined minimum stabilization height. An approach that does not meet the criteria at this point, or becomes unstable below this point, requires an immediate go-around— which means climbing to a safe altitude to determine the next course of action. On that fateful day in August 2011, the First Air pilots initiated a go-around, but it was too late.
Flight crews are required to stabilize approaches to runways for a number of reasons. Landings will be more consistent and predictable. Flight crews also have more time—and more attention—to monitor key elements such as communications and systems operation, thereby boosting their situational awareness. And at the heart of all of this is safety. Establishing and stabilizing the key variables in advance means fewer last-minute adjustments, which helps minimize workload during this critical phase. So when flight crews reach the pre-determined point where they must decide whether to proceed with the landing or carry out a go-around, they have more space—and time—to do so.
But this didn’t happen on August 20, 2011. The investigation into this accident highlights that there are too many unstable approaches that continue to a landing—some resulting in tragedy. Because current defences have proven less than adequate, and unless further action is taken, the risk of landing accidents will persist. That is why the Board issued a recommendation that: Transport Canada require airline operators to monitor and reduce the incidence of unstable approaches that continue to a landing.
If air operators take a hard look at addressing unstabilized approaches, this will hopefully mean safer landings for everyone.
Brian MacDonald has 31 years of aviation experience. Prior to joining the TSB he spent 23 years in the Royal Canadian Air Force as a pilot. Brian likes kayak camping, is an avid cyclist, and has competed in multiple triathlons.
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