CEN21LA351

The pilot reported that after takeoff in the experimental airplane, he noticed that all four cylinder head temperatures (CHT) were higher than they should have been as indicated on the engine monitoring device. He noticed that the CHT never stabilized and never decreased in temperature after the takeoff. The pilot attempted to reduce the high CHT with the throttle and mixture and the CHT kept rising. The pilot decided to return to the departure airport. During the flight back to the airport, the CHT still kept rising, and the engine ceased producing power. The pilot maneuvered the airplane for a forced landing to an open grass field surrounded by rolling prairie and trees. During the forced landing, the nose wheel and the main landing gear collapsed, and the airplane came to rest on the fuselage. Postaccident examination of the landing brake actuator revealed that it likely failed due to compressive overload on the actuator while positioned in the fully extended position. The actuator extension tube was found positioned about midway between the extended and retracted positions The flanges on the nut were fractured in overstress consistent with a compression overload. The brush that is normally attached to the nut above the flange was found in the fully retracted position, indicating that after the nut flanges fractured, the extension tube likely moved to the fully retracted position, pushing the brush along with it. Based on the examination of the landing brake actuator, the landing brake was likely fully extended at the time of the accident. The extended landing brake would have blocked airflow to the engine, causing the engine to overheat and cease producing power. If a cockpit indication system for the landing brake had been installed, the pilot likely could have known the status of the landing brake during the flight and thus retract it. It is likely that the pilot either forgot to retract the landing brake after the previous landing or the pilot may have inadvertently activated it before the loss of engine power. Based on the available evidence it could not be determined exactly when the landing brake was deployed.

On August 2, 2021, about 1554 mountain daylight time, a Cozy Mark IV airplane, N1361S, sustained substantial damage when it was involved in an accident near Rushville, Nebraska. The commercial pilot and passenger sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that after takeoff in the experimental airplane, he noticed that all four CHT were higher than they should have been as indicated on the engine monitoring device. He noticed that the CHTs never stabilized and never decreased in temperature after the takeoff. The outside air temperature was 91° F, and the airplane was traveling about 130 kts after the takeoff. The pilot attempted to reduce the high CHTs with the throttle and mixture and the CHTs kept rising. The pilot decided to return to the departure airport. During the flight back to the airport, the CHTs still kept rising, and the engine ceased producing power. The pilot maneuvered the airplane for a forced landing to an open grass field surrounded by rolling prairie and trees. During the forced landing, the nose wheel and the main landing gear collapsed from impacting the field, and the airplane came to rest on the fuselage. The pilot and passenger were able to egress from the airplane without further incident. The airplane sustained substantial damage to the composite fuselage. The pilot reported the airplane was “about topped off” with fuel prior to the cross-country flight and there was 44 gallons of 100LL fuel onboard during the takeoff. The airframe was equipped with a parachute, which was not activated during the emergency sequence. Postaccident examination of the airplane established flight control continuity and airframe to engine control continuity. The landing brake, also called the airbrake (located on the bottom of the fuselage, forward of the engine) was examined. Power was turned on to test functionality from the cockpit switch. The landing brake would not fully extend. Full extension is about a 45°angle downwards away from the fuselage. Impact damage such as scraping was observed on the underside of the landing brake. The actuator extension tube had play in it when the landing brake door was moved by hand. The airplane, which was classified as experimental, was not equipped with a landing brake indicator system in the cockpit, nor was it required to be. Postaccident examination of the landing brake actuator at the National Transportation Safety Board Materials Laboratory found the extension tube was positioned about midway between the extended and retracted positions. The nut inside the actuator was found positioned against the lower mechanical stop in the fully extended position. The flanges on the nut were found fractured. No evidence of any preexisting damage or cracking was observed. The brush that is normally attached to the nut above the flange was found in the fully retracted position. Examination of the engine revealedinternal engine continuity and no signs of a fire. The plastic thrust buttons on the rocker shafts were found melted. An exemplar owner’s manual from a Cozy Mark IV discusses the landing brake and states in part: A drag device is used to allow a steeper approach and to provide more deceleration in the flare. This belly-mounted brake is deployed by an electric switch on the lower center instrument panel. It is normally extended on final approach after gear extension and left down until after landing. Maximum allowable speed with the airbrake down is 90 KIAS. The brake does not affect stability, canard stall speed, or canard stall characteristics, and has only a mild effect on pitch trim. The brake significantly interferes with the airflow passing into the engine cooling NACA duct and engine temperatures will likely exceed safe limits if the throttle is set above 1,500 RPM with the brake extended.