N56466

On May 27, 2024, at 1145 central daylight time, a Piper PA-28, N56466, was substantially damaged when it was involved in an accident near Taylor, Texas. The pilot and one passenger sustained minor injuries, and the other passenger was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that during the carburetor heat check on the engine run up, the engine sounded like it backfired and then lost rpm. A second carburetor heat check was performed, and the engine operated normally.

The pilot reported that there was a decrease in engine rpm during initial climb after takeoff. He verified that the engine controls were full forward and executed a forced landing in a field. During the forced landing, the airplane struck the top of a berm, which resulted in substantial damage to the fuselage.

A review of the maintenance records revealed no entries germane to the accident. A visual examination of the engine revealed several discrepancies. The No. 3 cylinder exhaust pipe was missing a mounting stud and associated hardware. The gascolator was not safety wired appropriately; the gascolator fuel bowl was impact damaged. The carburetor heat valve operated normally but its mounting shaft exhibited excessive play. Additionally, the carburetor heat valve’s range of motion was limited due to impact damage to the assembly.

During the examination before the engine run, the spark plugs were noted to be black and sooty consistent with carbon fouling. Several of the spark plugs showed signs of wear; the center electrodes were football shaped. The cylinders were examined using a lighted borescope; the tops of the cylinders displayed a blackened appearance that was consistent with engine operation with a rich fuel-air mixture.

Six engine test runs were conducted; the engine started normally for all six engine test runs. The magneto checks were unremarkable. During the course of the engine test runs the throttle was moved from idle to full power, and vice versa, in both a smooth manner and an abrupt manner numerous times. The engine did not hesitate or stumble during any of these events.

During one engine test run, the carburetor air inlet hose was installed to replicate a collapsed or partially collapsed condition in flight. The installation of the hose was not documented in the maintenance records provided. The damaged engine cowlings and engine mounts prevented assembly of the complete system. The tube was attached to the carburetor heat box and hung loose instead of being hooked to the engine cowling. The engine started normally. The cuffed end of the intake tubing folded inward causing a restriction in the airflow to the engine. The engine operated 100-200 rpm lower than the previous engine test run. The loss in rpm could be restored through use of the mixture lever, but the lever was near the idle cut-off position to accomplish it.

The carburetor air inlet hose on the accident airplane was removed and sent to Piper Aircraft for examination to determine if it was the correct part. The results of the examination showed that it was not the correct part. The accident airplane carburetor air inlet hose was likely fashioned from a longer section of tubing that was not made to the same specifications as the one offered in the Piper Aircraft parts catalog.

The airplane manufacturer compared a carburetor air inlet hose from their stock to the to the one that was installed on the accident airplane and performed other checks to compare both against the drawing specifications. The stock part had a cuffed end on the hose and the wound wire stiffener in the hose ended where the cuff began. The end of the stock hose was uniformly cut. The accident airplane’s air inlet hose had indications that the wire originally went all the way to the end of the hose. The end of the accident airplane hose was uneven indicating it was likely cut by hand from a larger section of hose (see Figure 1).

Figure 1 – comparison of stock hose (right photo) to accident airplane’s

installed hose (left photo). Photo courtesy of Piper Aircraft.

The wall thickness of the hose on the accident airplane measured 53% thinner than the correct part. This was noted as a likely indication that the hose was single ply instead of double ply material. This was important as the correct part is rated for a negative pressure of -24 inches of mercury (in. Hg).

FAA Special Airworthiness Information Bulletin (SAIB) CE-114-23 was published August 6, 2014, regarding carburetor air inlet hoses on Piper Aircraft, Inc. (Piper) Models PA-28, PA-32, PA-34, PA-44, and PA-46 series airplanes. The SAIB cited an accident where the carburetor air inlet hose had not been approved for the airplane’s type design and had collapsed and restricted airflow to the engine resulting in a loss of engine power. The SAIB recommended owners of the affected models inspect their airplanes to verify an approved Piper carburetor air inlet hose was used and in serviceable condition.

A review of National Transportation Safety Board Case Analysis and Reporting Online (CAROL) data showed that since the date of the SAIB’s publication there were three additional accidents (ERA17LA128, CEN17FA139, CEN22LA377) where the carburetor air inlet hose was causal or potentially causal to an engine power loss event.