Kennesaw, GA, USA
N623W
AMERICAN AA-1
The pilot reported that after starting the engine he obtained the current weather conditions and then requested taxi clearance from ground control for the 10-minute flight. After takeoff, while about 500 ft above ground level (agl), the engine momentarily reduced to about 800 rpm and then abruptly returned to full power. The pilot began to turn back toward the airport and contacted the airport control tower and advised that the airplane lost power, but it had come back and he needed to get on the ground. The tower controller provided instructions to return and asked the pilot to restate the problem. The pilot advised that the airplane lost full engine power, and it was “cutting in and out.” The engine then reduced to idle before “quitting entirely.” The pilot attempted to troubleshoot the issue by using the fuel pump, switching fuel tanks, and checking the mixture. He did not report if or how he applied carburetor heat. He determined the airplane would not reach the runway and selected a nearby road for a forced landing. During the approach to the road, the airplane impacted a wire before it came to rest in the grass median. The pilot stated that he performed the engine runup and his instrument checks while “on the taxi down to runway 27.” The amount of time the engine was running while on the ground could not be determined; however, the summary of Federal Aviation Administration (FAA) air traffic control communications indicated that about 3 minutes elapsed between the request for taxi and the clearance for takeoff. The weather conditions reported at the departure airport near the time of the accident included a temperature of 14°C and a dew point 7°C, with a calculated relative humidity of 63%. These conditions were conducive to serious carburetor icing at cruise power settings. The likelihood and severity of carburetor icing is increased at the lower power settings that would have been used while on the ground. The pilot did not report if or how he applied carburetor heat during the ground operations. Typically, in general aviation operations, the before-takeoff checklist is completed in a run-up area or near the hold-short line before the airplane takes the runway for takeoff. In this case, the pilot apparently performed the before-takeoff checklist while taxiing for takeoff. During the engine run-up, he might have overlooked performing the carburetor heat check, or he performed the check so quickly that it did not have any practical effect on ice building up in the carburetor. Although a check of its operation is part of the engine run-up checklist, had the carburetor accumulated a significant amount of ice that check may not have been sufficiently long enough to completely melt it. During the postaccident examination of the airplane, it was noted that one of the four leads of the right magneto did not spark when the drive coupling was rotated. It is likely that the anomaly was due to impact forces; if not, the faulty condition would have been detected during the magneto check during the engine run-up. Additionally, a faulty lead on one magneto would not have resulted in a complete loss of engine power as reported by the pilot. Otherwise, the postaccident examination of the airplane did not reveal any mechanical anomalies that would have precluded normal engine operation. Given the weather conditions that were conducive to serious carburetor icing at cruise power, the pilot’s reporting of a loss of engine rpm and the subsequent “cutting in and out” of the engine, the loss of engine power was likely due to the accumulation of carburetor ice.
On April 7, 2022, at 1002 eastern daylight time, an American AA-1, N623W, was substantially damaged when it was involved in an accident near Kennesaw, Georgia. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the purpose of the flight was to return the airplane to its base and that it would be about a 10-minute flight. After he performed a preflight inspection, he started the engine, obtained the current weather conditions, and requested taxi clearance from ground control. The pilot, in his written statement, stated that, "I completed my engine run-up and instrument checks on the taxi down to runway 27. I advised the tower that I had completed my before takeoff checks and asked for an intersection departure as I do not need to use the entire runway for such a small aircraft.” During the takeoff roll he noted that all the engine instruments were “in the green” and the airplane lifted off with no issues. After takeoff, when the airplane reached an altitude of 500 ft agl, the engine momentarily decreased to about 800 rpm then “abruptly” increased back to full power. The pilot turned back toward the airport and communicated the problem to the control tower. The engine then reduced to idle before “quitting entirely.” He attempted to troubleshoot the issue by using the fuel pump, switching fuel tanks, checking the mixture, “basically anything to do with fuel.” However, the engine did not restart. He determined the airplane would not reach the runway and selected a nearby road for a forced landing. During the approach to the road, the airplane impacted a wire before it came to rest in the grass median. A review of an FAA summary of air traffic control communications revealed that the pilot advised the control tower that the airplane lost power, but it had come back, and he needed to get on the ground. The tower controller provided instructions to enter a right downwind for runway 27 and asked the pilot to restate the problem. The pilot advised that he lost full engine power, and it was “cutting in and out.” The tower controller cleared the pilot to land on either runway, and the pilot advised that he would not be able to make the runway and would be landing on a road. At 0950, the weather reported at the departure airport, Cobb County International Airport-McCollum Field (RYY), Kennesaw, Georgia, included a temperature of 14°C and a dew point 7°C. The calculated relative humidity at this temperature and dewpoint was 63%. Review of the icing probability chart contained within FAA Special Airworthiness Information Bulletin CE-09-35 revealed the atmospheric conditions at the time of the accident were "conducive to serious icing at cruise power." The length of time the engine was running on the ground could not be determined; however, the summary of FAA air traffic control communications indicated that about 3 minutes elapsed between the request for taxi and the clearance for takeoff. The pilot did not report details about carburetor heat use during the engine run-up or any other time before takeoff; however, a check of its operation is part of the engine runup procedure prescribed in the owner’s manual. According to FAA Advisory Circular 20-113, "To prevent accident due to induction system icing, the pilot should regularly use [carburetor] heat under conditions known to be conducive to atmospheric icing and be alert at all times for indications of icing in the fuel system." The circular recommended that when operating in conditions where the relative humidity is greater than 50% "…apply carburetor heat briefly immediately before takeoff, particularly with float type carburetors, to remove any ice which may have been accumulated during taxi and runup." It also stated, "Remain alert for indications of induction system icing during takeoff and climb-out, especially when the relative humidity is above 50 percent, or when visible moisture is present in the atmosphere." The pilot did not report if or how he applied carburetor heat when the engine began to lose power. According to the airplane owner’s manual, in the event of an engine failure, the pilot should check that the master switch is ON, the magneto switch is set to BOTH, the mixture set to RICH, the fuel selector set to the fullest fuel tank, and the carburetor heat set to ON. In another section, the owner’s manual advises that carburetor ice can occur at any time, and that “The first indication of carburetor ice … should be a slight drop in engine RPM. Slight engine roughness may or may not accompany this engine RPM drop.” The manual suggests that if carburetor ice is suspected the pilot should “slowly apply full carburetor heat. Engine roughness may then occur due to an overrich mixture or water from the melting ice.” Examination of the airplane at the accident site by an FAA inspector revealed that the airplane sustained substantial damage to both wings, the right elevator and horizontal stabilizer, and the rear section of fuselage forward of the horizontal stabilizer. A postaccident examination of the airplane was performed at a salvage facility by an NTSB investigator. The engine oil dipstick indicated 4 quarts of dark-colored oil present. There was no evidence of oil leakage on or around the engine. The engine case was uncompromised. The top spark plugs were removed. The electrodes were normal in wear and color when compared to a Champion Check-a-Plug chart. Engine internal continuity was confirmed by manually turning the crankshaft with the propeller. Compression and suction were observed on all four cylinders when rotated through. The valves operated normally during crankshaft rotation. Continuity was confirmed to the accessory section. The interiors of the cylinders were examined with a lighted borescope. Light surface rust was observed on the cylinder walls. The piston heads and the exhaust and intake valve heads were normal in appearance. The engine magnetos were removed and tested by manually turning the drive couplings. The left magneto produced a spark at all leads when rotated. The right magneto produced spark at 3 of the 4 leads. All fuel lines forward of the engine firewall were secure and in good condition. The wings had been previously removed and were not present, which precluded examination of the fuel system components within them. The electric airframe fuel pump and the mechanical engine-driven fuel pump operated normally. Fuel dripped from the engine-driven fuel pump when it was actuated by hand. The carburetor was removed for examination. The mixture and throttle connections were secure, with no binding noted. The bowl was clean and dry. The blue composite floats were intact and uncompromised. The carburetor inlet fuel screen was clean, dry, and unobstructed. The air intake to the carburetor was free of obstructions. The propeller remained attached to the crankshaft. One blade was bent aft about 10°, with some “S” bending, leading-edge damage, and chordwise scratches. The other blade was bent aft about 70° with no “S” bending noted.
A loss of engine power due to the formation of carburetor ice.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
