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If you're slow and over-banking during a base-to-final turn, an unrecoverable stall/spin at low altitude can happen.
Overshooting final is a leading cause for accidents in the traffic pattern. Most pilots immediately recover from the warning signs of the fatal base-to-final stall/spin. The pilot below wasn't so lucky...let's take a look at why.
On March 20th, 2008, a pilot landing at the Aero Plantation Airport (NC21), near Waxhaw, North Carolina, experienced strong tailwinds on the base leg of his traffic pattern. As he flew a Cirrus SR22 into the pattern, maneuvering for a left base turn to Runway 6, the nearest weather station (KEQY, about 6 miles away) reported winds from 310 degrees at 11 knots, gusting to 20 knots.
According to the NTSB, "this combination of wind direction and speed created a situation where ground speed was higher than airspeed for the turn from base leg to final. The higher ground speed would have required a larger turning radius than normal, or an increased angle of bank than if the winds were calm."
Although not mentioned in the NTSB report, it's important to note the size of this airport's runway. At only 2,400 feet by 60 feet, NC21 has a relatively small runway.
Small, thin runways like this can create the illusion that you're flying at standard traffic pattern distances, when in reality you're much closer to the runway. Depending on your airplane, altitude, and speed, a normal downwind for light aircraft is flown at approximately 1/2 to 3/4 of a mile away from the runway. Contrary to small runways, at airports with larger runways, you're more likely to fly patterns at a greater distance from the runway. Simply, this is because the runway looks larger in your field of view. Add the fact that strong crosswinds would've been pushing this pilot even closer to the runway, creating a very challenging base-to-final turn.
According to the NTSB, data extracted from the aircraft's GPS unit last showed the Cirrus at an altitude of 838 feet. Vertical speed was -444 feet per minute, with an indicated airspeed of 60.3 knots. Pitch attitude was 4.98 degrees nose-up and there was a left roll of -31.73 degrees. "These parameters indicate the airplane had or was about to enter the early phase of an aerodynamic stall" (NTSB). Click here to read the full NTSB accident narrative.
Keep in mind, the data listed above was just the last recorded information. It's likely that to compensate for a strong tailwind, the pilot continued banking the aircraft to line up on final approach. At an increasingly high bank and slow airspeed of 60 knots, the Cirrus SR22 was entering a stalled condition.
The minimum demonstrated loss of altitude when deploying the Cirrus Airborne Parachute System (CAPS) in level flight is 400 feet - or 561 feet for a Cirrus G5 aircraft. And the minimum demonstrated loss of altitude in a spin is 920 feet, or 1081 feet for a G5 airplane when deploying CAPS. In fact, Cirrus' procedures recommend deploying CAPS at a minimum altitude of 500' (600' for G5), unless a survivable landing can't be made. In this accident, "CAPS was found deployed and the CAPS rocket motor propellant was expended... The CAPS rocket motor was found entangled in tree branches, approximately 25 feet above the ground, at a point approximately 35 feet behind the main wreckage."
Successful deployment of CAPS at this low altitude would've been nearly impossible. And recovery from an accelerated stall condition, if progressed into a spin, would have been nearly impossible with such little altitude for many other airplanes.
According to the NTSB, "the wreckage was located approximately 2,000 feet short of the approach end of Aero Plantation Airport's runway 6, in a wooded area behind a residence... Broken tree branches were noted at the top of a 70-foot tall tree in the back yard of the residence. Additional broken tree branches were noted along the debris path leading to the main wreckage."
If it's a windy day, pay extra attention to where the wind is coming from and how that might affect your turning radius in the traffic pattern. Don't let small runways fool you into flying a tight traffic pattern. And NEVER get slow on a base-to-final turn. Going around to try again is always the best option.
Want to know more? Read more tips on how to prevent disaster in the traffic pattern.
According to AOPA, the NTSB released its "Most Wanted" list of transportation safety improvements on November 14th. The list included general aviation loss of control. The University of North Dakota, in partnership with the AOPA Air Safety Institute, announced that it is studying the use of a continuous turning approach or "circular pattern" as an alternative to the traditional "box" or rectangular traffic pattern.
For years, airlines, the military, and warbird pilots have relied upon the continuous approach turn. This is the hypothesis being reviewed:
"In contrast with a rectangular pattern, a continuous turn from downwind to final may provide for increased stability, reduced pilot workload, and a constant bank angle throughout the maneuver, helping pilots better manage angle-of-attack variances. Additionally, the use of a continuous turning approach has the potential to reduce the likelihood of overshooting a runway during base-to-final turns, a scenario that has resulted in multiple stall/spin accidents due to aggressive corrective maneuvering."
We won't know the results of the study until early next year, but it's possible that changing the way we treat base-to-final turns could make a huge difference on stall/spin accidents, especially in conditions that led to the accident above.
What do you think of continuous approaches? Tell us in the comments below.
Swayne is an editor at Boldmethod, commercially licensed pilot with multi-engine and instrument ratings, and a commercial aviation student at the University of North Dakota. He's the author of the articles, quizzes and lists you love to read every week. Swayne's experience ranges from international flights in a King Air F90 to ferrying a 1943 Grumman Widgeon across the country. You can reach Swayne at firstname.lastname@example.org, and follow his flying adventures at http://www.swaynemartin.com.