The private pilot reported that, about 35 minutes into the personal cross-country flight, the experimental, amateur-built airplane’s alternator field toggle switch/circuit breaker tripped. He reset the switch, and all systems appeared normal.
About five minutes later, the switch tripped again, and he cycled the switch.
About two minutes later, he noticed that the engine manifold pressure was dropping, along with the airplane’s airspeed, consistent with a partial loss of engine power.
The engine then experienced a total loss of power when he was maneuvering for an emergency landing to a nearby airport.
The Glasair Super IIS landed short of the runway in Yuma, Arizona, sustaining substantial damage to the aft fuselage.
The engine had been installed about 91 flight hours and 5 months before the accident, and a condition inspection was completed the same month of installation.
Maintenance records indicated that during the period between the engine installation and the accident, maintenance was limited to routine oil changes, magneto timing adjustments, the replacement of exhaust gas temperature and cylinder head temperature probes, and the installation of a replacement alternator.
Post-accident examination of the engine revealed that the throttle linkage had detached from the throttle arm of the fuel injection servo. The rod end bearing for the linkage and the throttle arm were intact and undamaged, but the connecting bolt and its associated washers, castellated nut, and cotter pin were missing.
The butterfly valve within the throttle body was in the closed position, and the throttle lever in the cabin was in the full forward (open) position.
It is likely that the bolt securing the linkage had not been sufficiently tightened and secured with a cotter pin during the installation and that the error was not detected during the subsequent condition inspection.
The investigation determined that the electrical system malfunction was unrelated to the loss of engine power.
Probable cause: A total loss of engine power as a result of the detachment of the throttle linkage from the throttle arm of the fuel injector servo due to an insufficiently tightened and secured bolt and the subsequent inadequate maintenance inspection.
NTSB Identification: WPR18LA250
This August 2018 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Another example here of why Aviation runs more on trust than mere money. 99% of the potential for accidents is out of sight of the pilot in every pre-flight… waiting to be ‘discovered’ when some mysterious loss of power, control, or… occurs in flight.
That’s for sure. There was an incredible story not long ago about an engine failure due to a paper towel left inside the engine! A paper towel!
Looking at a number of pics of fuel servos, none have any bias spring on the throttle shaft.
My Marvel carb has the coil spring that will open the throttle wide open if the cable disconnects.
It is most likely that the cotter pin was not installed on the castle nut on the throttle connection to the servo lever. Or, the wrong hardware was used.
The throttle on the typical Marvel carburetor is spring-loaded to go to full throttle. This is a safety feature – in case the linkage disconnects, the engine will continue to produce power instead of falling off to idle. Doesn’t a throttle body have this same feature?