In February 2010, a CESSNA T337G Skymaster made a low pass over the runway at Farmingdale, New Jersey. As it pulled up, a six-foot piece of the right wing broke away; the ensuing crash, before the eyes of friends and relatives for whose benefit the pass was being made, killed all five aboard.
In August of the same year, in Saltsburg, Pennsylvania, a Beech Baron crashed into a house. The pilot-owner of the Baron and a flight instructor died, and the house was destroyed by fire.
Both airplanes had been modified under multiple STCs, and the NTSB concluded that interactions between various modifications could have played parts in both crashes.
The pilot of the Baron, a 1982 Model 58, had owned the same airplane 22 years earlier. He had sold it, moved up to a Cessna Citation 510, and four days before the accident purchased his old Baron again. In the interval, the airplane had been modified with more powerful engines — 300 hp rather than the original 285 — four-blade props, winglets, and vortex generators on the wings and vertical stabilizer.
The purpose of the vortex generators was to lower the minimum control speed by delaying the stall and improving the effectiveness of the rudder. Normally, the minimum control speed of the 58 is 81 knots; the VGs dropped it to 74, and the modification included replacing the original airspeed indicator with one marked to reflect the new, lower Vmc.
The more powerful engines were installed later. One of the consequences of the added power was an increase in Vmc, which rose from 81 to 87 kias on the stock airplane. In the absence of flight test data, the NTSB noted that the Vmc of the VG-equipped airplane was likely to have been similarly increased by the added engine power; but the holder of the engine-replace-ment STC was not required to determine a new Vmc for every Baron variant, only for the standard model. The STC instructions did include a direction to “mark instruments in accordance with Flight Manual Supplements for the appropriate model,” but it was probably unclear to the installer what the instruction meant in the particular case of the VG-equipped Baron, and the FAA provided no guidance; so the airspeed indicator with the red Vmc line at 74 knots remained unchanged.
The Baron’s radar track, as well as the statements of witnesses and the evident purpose of the flight, suggested that it was performing a Vmc demonstration at around 4,000 feet when the spin occurred. The maneuver would involve reducing power on the left engine to idle, bringing the right engine to full throttle, and gradually reducing speed until it was no longer possible to hold heading.
As far as NTSB investigators could determine, the pilot may not have flown a reciprocating-engine airplane for three years prior to the accident. They noted too that he was required to have a second pilot with him in the Citation, which is eligible to be flown single-pilot, because he did not meet single-pilot proficiency requirements. There were indications that his shortcomings were related to speed control, which could, of course, be involved in a Vmc-related mishap.
A possible contributing factor was the airplane’s throw-over control column, which might have impaired the instructor’s ability to prevent the spin or recover from it. Another contributing factor was “the lack of guidance by the Federal Aviation Administration for an installer of a supplemental type certificate (STC) modification to determine the interrelationship between all STCs incorporated into an aircraft.” At the end of 2011, the FAA partially remedied the omission with an airworthiness directive (AD) mandating that, in the absence of other information, the Vmc for the VG-plus-engines mod would be the VG-equipped Vmc multiplied by the ratio between the re-engined Vmc and the stock Vmc — in other words, 74 x (87/81), or 79.5 kias.
It should be noted that Vmc-related spins are by no means unheard of in the stock Baron or in its precursor the Travel Air, and so the fact that this Baron had a misleadingly marked airspeed indicator, while suggestive, cannot be absolutely linked to the loss of control.