Pilots Tell Investigators Plane Stalls At Higher Speeds Than Indicated

(EDITOR'S NOTE: In regards to the discrepancy between speed arc ranges on the airspeed indicator of the Zlin Savage, and the speeds noted in two separate sections of the aircraft's operating manual,  ANN originally reported such arc markings are not required on airspeed indicators on S-LSA, based on the following statement in the NTSB report:

"The ASTM standards do not outline requirements for airspeed instrument markings. ASTM 2245-04 (under which the accident airplane was designed) Section 8.2.1 only requires that the airplane shall be designed with an airspeed indicator."

The EAA's Earl Lawrence -- who chaired the ASTM rules committee on the matter -- responded Wednesday the NTSB has it wrong. "[Section ] 9.10.1 Airspeed indicator range markings" clearly means to me that there are suppose to be airspeed instrument markings, it's even in the section that says "required placards and markings."

Lawrence adds he has called the NTSB's attention to the incorrect statement. ANN regrets the error.

The National Transportation Safety Board says improper arc markings on the airspeed indicator of a Zlin Savage light sport aircraft contributed to the August 2007 loss of the plane near Mosquero, NM that claimed the lives of the two persons onboard.

According to the Board's Probable Cause report, the pilot's failure to maintain adequate airspeed was cited as the primary cause of the crash, which killed pilot Jeffrey Lane and passenger Ryan Hartley. The wreckage displayed evidence of a stall/spin-type accident; data recovered from the Garmin GPS396 onboard the plane showed the aircraft entered a steep, spiraling descent during a left 360-degree turn from about 350 ft. AGL.

The Board also noted discrepancies between the arc markings on the plane's airspeed indicator, versus differing values listed in two separate sections of the aircraft's flight manual. Investigators say the aircraft's airspeed indicator included markings denoting the white arc extending from a lower range (Vso, or stall speed at maximum takeoff weight, in landing configuration) of 36 mph, through the upper (maximum speed with flaps extended) limit of 71 mph.

Those markings do not match up with the white arc range noted in the "Airspeeds" section of the aircraft's operating manual -- 31 mph through 69 mph -- nor do they match what the manufacturer states is the VSO in the "Performance" section of the flight manual, which is 38 mph.

Furthermore, the NTSB cited several pilots who stated "they had experienced stall conditions in the Zlin Savage well above the published stall speeds.

"One flight instructor stated that while climbing out he encountered what he felt was a downdraft and the airplane 'began an enormous descent,'" according to the Board's report. "He stated that the airplane handled as though it 'were in a deep and unrecoverable stall.' Another flight instructor with extensive experience in various S-LSA aircraft experienced a stall in the Zlin Savage around 58 mph, well above the published stall speed. He stated that during this particular flight he was climbing in smooth air, wings level."

Not all pilots interviewed by the NTSB agreed with those assessments, however. Other Zlin Savage owners and pilots told the Board the plane (type shown below) exhibits docile stall behavior, at slow speeds.

According to Lane's logbook, the pilot had over 3,400 hours flight time, with at least five hours in the accident airplane. Eight months before the crash, Lane had completed a flight review at Flight Safety International.

FMI: Read The NTSB Probable Cause Report