COATESVILLE, PA, USA
N465W
SILVA SEAWIND 3000
THE KIT PLANE WAS ON A TEST FLIGHT WITH A HARTZELL LIMITED PRODUCTION/CONSTANT SPEED/NON-FEATHERING/FULL REVERSING PROP. THE PILOT STATED THAT IN THE 1ST POWER-OFF GLIDE, HE SET THE THROTTLE TO IDLE & THE PROP TO LOW PITCH; ABOUT 10 TO 15 SEC LATER, THE ENGINE RACED & THE PROP APPEARED TO GO TO ZERO PITCH. HE SAID MOVEMENT OF THE PROP CONTROL & THROTTLE HAD NO EFFECT; THE PASSENGER SAID THE THROTTLE WAS ADVANCED & RPM OVERSPED EVEN MORE. ALTITUDE COULD NOT BE MAINTAINED & A FORCED LANDING WAS MADE ON ROUGH TERRAIN. AN INVESTIGATION REVEALED THE PROP BLADE ANGLE LIMITS WERE WITHIN THE PRESCRIBED -15 TO +26.2 DEG LIMITS. THE LOW PITCH BLADE ANGLE WAS SET FOR 3.7 DEG, BUT SPECIFICATIONS FOR TYPICAL HARTZELL & LYCOMING ENGINE COMBINATIONS HAD LOW PITCH BLADE ANGLES RANGING FROM 12 TO 13.5 DEG. TESTING OF THE PROPELLER DISCLOSED THAT THE CENTRIFUGAL LOW PITCH START LOCKS WOULD NOT ENGAGE, IF THE GOVERNOR OIL PRESSURE REMAINED AT OR ABOVE 120 PSI AFTER START LOCK DISENGAGEMENT.
On April 3, 1993, at 1055 eastern standard time, a kit built Sea Wind 3000, N465W, owned by S.N.A. Inc., and piloted by Charles R. Mills, was substantially damaged when it impacted the ground during a forced landing, near the Chester County Airport, Coatesville, Pennsylvania. The pilot was not injured and the passenger received minor injuries. Visual meteorological conditions prevailed and no flight plan had been filed for the flight operating under 14 CFR 91. In the NTSB Form 6120.1/2, the pilot stated: "...After about 1 hr. [hour] of recording climbs, approaches to stalls, ect., I decided to try a glide, with power to idle, and prop [propeller] control to low pitch, at 3,000' [feet] MSL [mean sea level]. About 10 to 15 seconds after bringing the throttle to idle and prop control to low pitch, the engine raced and the prop appeared to go to zero pitch. Movement of the prop control and throttle had no effect. I immediately turned to a downwind heading for a forced landing on runway 29, but I did not have enough altitude to make the runway and touched down in rough terrain..." The airplane was configured with an Hartzell constant speed, non feathering, full reversing propeller. The propeller was a limited production system, of which only eight were shipped from Hartzell. Four of the propeller systems were sent to airplane manufactures for experimental purposes, two of which went to Seawind, and four were sent to LTA (lighter than air) manufactures. This was the 4th hour of flight testing the kit built single engine seaplane, with this combination of engine and propeller. Specifications for Hartzell propeller and Lycoming engine combinations, show that standard single engine installations of the Lycoming IO-540, would have a low pitch blade angle ranging from 12 to 13.5 degrees. During the post accident investigation, all components of the propeller system were tested and found to be operational. The propeller blade angle limits were measured at Hartzell and found to be within the prescribed limits of -14 to 26.2 degrees. The low pitch blade angle was measured at 3.7 degrees. During the post accident investigation and after being informed about the low blade angle setting, Mr. Silva, the owner of S.N.A., discussed in a letter dated April 9, 1993, to Hartzell Propeller Inc., some of his observations during the initial testing, Mr. Silva stated: "...This would explain why we had to use excessively high RPM just to start a taxi operation. As Bob Mills and I both explained we also felt a hesitation (slow to roll) in takeoff. We also had trouble gradually reducing power on landing. There seemed to be no response and then a sudden wind milling of the prop pitching the nose up. All of this occurred at high RPM and very low throttle setting and low manifold pressure. When we were simulating approaches we did not throttle back very much and when the throttle was advanced the climb did ensue after a slight hesitation. However, when Bob Mills simulated a power off glide he throttled back to a much lower setting but still had high RPM. That is when it appeared that we went into zero (no power) pitch. We could not get it to change pitch after that point. Neither he or I think that we went into full reverse but we are not sure that we weren't slightly (a few degrees in reverse)..." A report prepared by Pratt and Whitney, discusses the basic operations of the constant speed propeller system. It describes a typical low pitch blade angle, for a reversing propeller, to be about 15 degrees with the throttle at idle. It also describes the region between 15 degrees and minus 5 degrees blade angle as the "Beta" range. In the textbook, Aerodynamics for Naval Aviators, it states: At small blade angles near the flat pitch position, the drag added by the propeller is very large. At these small blade angles, the propeller windmilling at high RPM can create such a tremendous amount of drag that the airplane may be uncontrollable. According to Hartzell Propeller Inc., the propeller blade low pitch stop setting of 3.7 degrees was set at Hartzell. In a telephone conversation with Mr. McCrady, a Hartzell design engineer, he stated he was not aware of why the blade angle was set at 3.7 degrees. He also stated that the blade setting would not have been provided to S.N.A. prior to the accident. Mr. McCrady stated that propellers are sent out of Hartzell with calculated settings based on the performance requested by the manufacture. After the initial installation and testing, the manufacture would adjust the setting as required. In a report by the FAA Inspector, who attended the propeller teardown at the Hartzell facility, he stated: "...A complete examination of the propeller and operating components was made...The governor was purchased separately...as a used item for this installation and was not the recommended model. No previous operating history was available. This additional testing discovered the propeller governor output pressures were outside the normal specified manufacturer's values. Hartzell...does not usually develop specific rigging /setup procedures/parameters to determine the propeller control output pressure limits for the airframe installation. This is usually defined by the airframe designer/manufacturer. The pressure outputs recorded as a result of this testing indicate that the propeller was not properly rigged for normal operation." "In summary, the propeller control assembly was examined and tested operationally at the Hartzell facility. The propeller control system operated as designed and functioned normally when set to average Hartzell specified governor control pressure output parameters. Hartzell Propeller has determined that it may be possible for the propeller to operate improperly if the governor control pressures are set abnormally high, as was this for instance. I informed Mr. Silva that due to the experimental nature and that this product was in research and development, the FAA does not determine methods by which development of the aircraft is accomplished. All design and test criteria is developed by the designing firm." The Hartzell Propeller Inc., Operator's Manual NO. 136 states: At start up a pressure too high will cause propeller to reach blade angles lower than low pitch stop setting. With pressure too high at low RPM (below 1000 RPM ) the stop collar would be able to overpower preloaded propeller spring and move low pitch stop unit before centrifugal locks could engage to prevent reversing (beta operation). The results would be that maximum RPM could be easily attained with much less than maximum throttle. In a letter from Hartzell Propeller Inc., to Mr. Richard Silva, it states: "In summary, my conclusion was that during the power off glide condition with full rated RPM selected on the propeller governor, the propeller moved to a position at or very near to the low pitch stop position of 3.7 [degrees] blade angle, resulting in a less than zero thrust condition...Cycling of the propeller pitch control lever under this condition would have had little to no noticeable effect on the propeller operation. Advancing the throttle above the idle setting would have increased the propeller blade angle to a thrusting mode of operation."
IMPROPER ADJUSTMENT SETTING OF THE PROPELLER PITCH CHANGE MECHANISM AND/OR PROPELLER GOVERNOR OUTPUT PRESSURE, WHICH RESULTED IN A LOSS OF POSITIVE THRUST AND A FORCED LANDING.
Source: NTSB Aviation Accident Database
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