Safety Pilot: Set-up stall

Accident at the airshow

August 1, 2013

safety pilotDistraction is almost always a factor during an accident sequence. Nowhere is there likely to be more distraction than when arriving at a fly-in where there are many more aircraft than usual to avoid. Pilots need to be on their game and recognize that even though special ATC procedures are in effect, standard aerodynamic rules still apply. In this loss-of-control accident, the NTSB’s determination was predictable. But there was also a systemic flaw, in my view, and the arrival procedure in use was the precipitating event.

Warbird/turbine arrival.

On the evening of July 27, 2010, a Hawker Beechcraft 390 (Premier 1A), N6JR, entered the Oshkosh, Wisconsin, area under visual flight rules, inbound from Ypsilanti, Michigan. Weather was not a factor in this accident. The pilot called in on the Turbine/Warbird Arrival, a published procedure used by jets and other high-performance aircraft during EAA AirVenture. At 6:11 p.m. Central Daylight Time (CDT) the control tower told the pilot to expect a left base to Runway 18R.

During AirVenture, a parallel taxiway east of Runway 18 is used for takeoffs and landings and is identified as Runway 18L. The main runway, normally identified as Runway 18, becomes Runway 18R with a displaced threshold of 1,300 feet, leaving 6,700 feet available for takeoffs and landings. This is necessary to avoid conflict with traffic arriving on Runway 27, located just to the north of Runway 18. Arriving aircraft receive clearance from the tower. Departing aircraft are handled by other controllers operating on a separate frequency designated as the mobile operations/communications workstation (MOOCOW). Who says the FAA has no sense of humor?

At 6:15 the jet was instructed to turn northbound onto a left downwind and had previously been cleared to land. Simultaneously, the MOOCOW controller advised a Piper Cub to line up and wait on Runway 18R. The Cub pilot acknowledged and requested an “angled departure to stay clear of faster traffic.” At 6:16 the MOOCOW transmitted, “Cub, uh, 18R cleared for takeoff as requested, cleared for immediate takeoff.”

The jet’s pilot was not monitoring the departure frequency, nor was he required to—and, as a result, he wasn’t aware of the Cub’s plan for an immediate left turnout after takeoff.

A tight turn.

Post-accident data from ATC recordings and onboard electronics showed the jet turning base leg as the Cub was cleared for takeoff. At 6:16:19, the jet pilot, seeing the Cub, transmitted to the tower, “Is, is, Six-J-R gonna be OK with this?” The tower controller responded, “Affirmative,” to which the pilot replied, “I don’t think so.” Presumably the pilot was uneasy about the runway being occupied. There was still time to abort the approach—and when that little voice inside says things are not looking good, listen to it!

At 6:16:21, the MOOCOW controller transmitted, “Cub, as soon as you’re airborne offset off the runway,” and at 6:16:33, advised the Cub pilot to, “Turn left off the runway, traffic short final behind you.” The jet was now turning short final.

At 6:16:35, the jet’s enhanced ground proximity warning system (EGPWS) announced “bank angle” continuously, indicating a steep bank. At 6:16:40 the pilot transmitted “Going around.” An amateur video showed the Premier pitched up at that time.

At 6:16:46, the tower controller acknowledged the go-around, stating, “Alright, Premier jet, uh, use caution for the, uh, traffic ahead on the upwind and, uh....” During this transmission, the CVR recorded an increase in engine sound during six seconds until 6:16:54. At 6:16:54 the EGPWS announced “bank angle” two more times. The engine sound remained steady until impact at 6:16:57. The CVR also captured a stall warning tone.

The jet overshot the runway as the bank angle increased from 32 to 43 degrees, with the left wing down. The airplane also descended from 185 feet to 37 feet above the ground during the turn to final (my emphasis). After the overshoot, the jet leveled momentarily for about six seconds before entering a climb. It reached 117 feet agl in a 30-degree left bank. Then the right wing stalled and it rolled 44 degrees right just before impact. The angle of attack was between 11 and 16 degrees and the maximum descent rate was 1,972 feet per minute.

Witnesses reported that the Piper Cub performed a short-field takeoff, offset after liftoff, and was airborne between Runways 18R and 18L as the Premier jet was turning base to final. The Premier hit right wing low and was destroyed. There was no fire, and the pilot and passenger suffered serious but non-life-threatening injuries.

Pilot and aircraft.

The jet overshot: The tight left turn onto Runway 18R, where the Piper Cub had just departed. It was airborne and flying between runways 18R and 18L as the jet was turning base to final. Illustration not to scale.

The Premier’s pilot, age 68, held an airline transport pilot certificate, with type ratings in the Cessna 525 (Citation) and the Premier, with a current second class medical.

The pilot had 9,095 hours total time with 6,930 hours in multiengine airplanes. He had flown approximately 1,425 hours in the Premier with 62 hours during the past 90 days, 17 hours during the past 30 days, and 1.5 hours during the previous 24 hours. His flight review was completed in the accident airplane on December 9, 2009.

There were no preimpact malfunctions on the jet. According to the aircraft flight manual, the procedure for a balked landing is to apply takeoff power and establish VREF (reference landing approach speed) and, after establishing positive climb, clean up the gear and flaps.

According to the NTSB, “The pilot reported that he initiated a go-around, increasing engine power slightly, but not to takeoff power, as he looked for additional traffic to avoid. He estimated that he advanced the throttle levers probably a third of the way to the stop and, as he looked for traffic, the stall warning stick-shaker and stick-pusher systems activated almost simultaneously as the right wing stalled. He did not recall hearing a stall warning horn sound.”

NTSB review and probable cause.

Because of AirVenture’s high-density traffic, special ATC and arrival procedures are in effect, which put big demands on pilots and controllers alike. There are multiple distractions when operating in close proximity to other aircraft.

The pilot stated that he decided not to land because of a perceived conflict with the departing Piper Cub.

Witness statements and data recovered from the Premier showed the Cub was already airborne, had turned left, and was clear of Runway 18R when the accident airplane turned from base to final. The Cub on the runway likely distracted the pilot from his primary task of flying his own aircraft.

The NTSB determines the probable cause of this accident as, “The pilot’s decision not to advance the engines to takeoff power during the go-around, as stipulated by the airplane flight manual, which resulted in an aerodynamic stall at a low altitude.”

A contributing factor.

Looking at root causal factors, there is some question in my mind about the safety of the VFR Rwy 18R Arrival, specifically since it requires turbine aircraft to make a tight, low-altitude turn immediately before landing to avoid the flow of traffic on Runway 27.

It works for warbirds and light aircraft, which tend to be more maneuverable and are often piston powered. But this is contrary to the stabilized approach concept that is essential to flying turbine aircraft safely—airshow or not. The usual recommendation is that large aircraft be in final landing configuration and stable (that includes being aligned with the runway) at 1,000 feet agl. For small aircraft we recommend 500 feet agl. I’ve flown through this particular arrival in jets several times during AirVenture, and I believe that the potential for a catastrophic loss of control at very low altitude is not worth the relatively minor reward of slightly expedited traffic flow.

The airshow environment is unforgiving and there are occasional mishaps, but some procedures give away most of the margin. It all depends on your risk tolerance. The notam mentions, “If your landing appears unsafe because of space, speed of preceding aircraft, or any other reason, go around.” A better procedure would be to offer straight in to Runway 27 to turbine aircraft.

As in so many cases, the lack of an accident beforehand doesn’t mean that an action is safe, merely that all the links in the accident chain did not connect. So, although the use of takeoff power would have prevented the accident, I will respectfully add a note of dissent to the NTSB’s findings that set this accident scenario in motion. My hope is that the FAA will consider turbine and twin arrivals to allow a less exciting but safer stabilized approach.

The 2013 VFR arrival procedures to Runway 18 remain unchanged from previous years.

Illustration by P.J. Loughran