According to the pilot, who is also the mechanic, he had not flown the Luscombe 8 “for some time.”
He performed the preflight inspection with no anomalies noted. The fuel tank was full of fuel, the fuel vent was checked, and he “sumped” the fuel tank.
The pilot started the airplane, taxied to the north end of the runway at the airport in Kingsbury, Texas, and performed the run-up procedure with no anomalies noted. As part of the run-up procedure, both magnetos, the carburetor heat, and the fuel system were all checked.
The airplane took off and the pilot noticed the engine was “performing very well.”
The airplane climbed to about 400 feet AGL and the pilot initiated a left turn.
About halfway through the turn, the engine sustained a total loss of engine power.
The pilot reported there was “no cough” or “no sputter” and the engine “just died.”
He attempted to troubleshoot the loss of engine power to no avail.
He maneuvered the airplane for a forced landing to an open field. The pilot then realized the airplane would not make the open field and maneuvered the airplane for a wooded area. The airplane came to rest in trees, sustaining substantial damage to the fuselage, both wings, and the empennage.
The pilot, who sustained minor injuries in the crash, was able to get out of the airplane on his own.
The pilot told investigators that when the engine lost power, it was operating at full power. He assessed that perhaps a short occurred in the ignition switch, which resulted in the loss of engine power.
A post-accident examination revealed that the airplane was not equipped with a starter. The ground to the key-operated ignition switch was found disconnected. The pilot surmised that he may have pulled off the ground lead when he removed the ignition switch from the panel.
The p-leads for the left, right, and both positions were checked with a multimeter. The readings for the p-leads varied from open to closed, along with varied ohm, or resistance, readings.
The ignition switch was then disassembled, and carbon tracking, a buildup of carbon that interfered with electrical continuity, was observed.
A substantial amount of carbon tracking was found inside the ignition switch, particularly on the contacts. The contacts in the ignition switch were then cleaned and the ignition switch was reassembled. The p-leads were checked again with a multimeter, the varied ohm readings were no longer present, and the ignition switch appeared to function normally with the multimeter.
There were no issues noted with the magnetos, the ignition harness, and the spark plugs. The magnetos are electrically independent, except at the ignition switch, and both magnetos produced spark when checked.
The pilot told investigators that while the ignition switch was not originally installed by the manufacturer, it had been in the airplane for over 40 years. He additionally reported that he had no previous issues with the ignition switch, the ignition switch was never overhauled, nor was he aware of an overhaul schedule for the ignition switch. According to the manufacturer, the maintenance requirements for the ignition switch are based on condition.
The FAA’s Aviation Maintenance Technician Handbook – Powerplant Volume 1 defines carbon tracking for an ignition system and states in part: “Flashover can lead to carbon tracking, which appears as a fine pencil-like line on the unit across which flashover occurs. The carbon trail results from the electric spark burning dirt particles that contain hydrocarbon materials. The water in the hydrocarbon material is evaporated during flashover, leaving carbon to form a conducting path for current. When moisture is no longer present, the spark continues to follow the carbon track to the ground.”
Probable Cause: A total loss of engine power due to a failure of the ignition switch from carbon tracking, which resulted in a forced landing and a subsequent impact with trees.
To download the final report. Click here. This will trigger a PDF download to your device.
This September 2022 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.
The NTSB has not done the aviation community any favors by not including any technical details regarding the type of switch, age of switch etc. Not showing photos of the carbon tracing is likewise a disservice.
The prevention of aviation accidents is aided by the sharing of information. In this instance there is no truly useful information shared in this NTSB report.
Now I’m going to have to spend some quality time with the ignition switch in my Luscombe to see if it might exhibit the same problem. After all, the switch is only 84 years old!
The docket, items 2 and 3 have all the info.
It is a Bendix switch , about 40 years old.
I had a 1946 Cessna 140 back in the early 70s It had switches for each Mag.
I am not completely following all of the terminology.
Is this a Rotary Type of magneto switch, L R B off ?
I have rotary type in my twin engine airplane. Off L R Both Start and there is no “security key”
Should I be removing and cleaning the switch?
So many accidents involving the rotary switches. I think they were designed in the 1950’s to be similar to cars.
A better design would be independent L/Off R/Off magneto switches and a separate starter switch.
I would pay for an STC and components to replace my rotary switches. I would not want a locksmith’s security key involved with operating my engines or cabin door in any way.
Independent magneto switches would have prevented the losses in this article and many others.
Any switch with sliding contacts can be subject to conductive contamination. So, I ‘d recommend cleaning the contact block and lubing it with Luberex grease, especially if it’s more than 15-20 years old
Most GA aircraft use a keyed mag switch, with ‘Off ,L ,R, Both, and later models with ‘Start’.
My old Cessna uses a separate pushbutton to activate the starter contactor.
Separate ‘snap action’ toggle switches would be more reliable, but the pilot would need to do the mag checks more carefully, and guards would be advised to prevent inadvertent moving the switch to the ‘off’ position.
“The pilot surmised that he may have pulled off the ground lead when he removed the ignition switch from the panel.”
Just a question .. with the ground wire removed, how was the ignition switch going to ground the P lead thus grounding the magnetos and shutting down the engine?
I worked at a Baltimore based Cessna dealer for 10 years. That Bendix and Gerdes switch AD (also a Cessna Service Letter) required running the engine and momentarily switching the key to “off”, while forcing it to the left. If the engine continued to run, the switch required replacement. With our fleet of 100-series Cessna aircraft, I found a few malfunctioning switches, but tried a different approach. Without removing all the switch wires, I took the switch halves apart, and found a black, greasy residue on the copper traces, and on the three tricornered contacts. This I cleaned up with a bit of acetone, then wiped the traces with a very thin coating of DC-4 compound. I put the tricornered contacts back, but in different locations to even out the wear, then reassembled the switch. Any problem was gone. I made an inspection note to service these switches at every annual inspection. Never had to replace a single switch.
Some older Bendix ignition switches are subject to AD 76-07-12 which calls for pre-flight checking of switch operation and references service information for detailed inspection. This style of switch has been the standard for GA piston aircraft for many years. Later, Gerdes developed a similar switch which is subject to AD 93-05-06, involving similar inspection and cleaning requirements.
Old twist-to-turn lever type Bendix Scintilla switches were used in even older airplanes that prove problematic when its primary function, that of providing and lifting a grounding source, is compromised by age.
This is a new problem to me.! As an electrical engineer, I know that the P-lead will see about a 300 volt spike when the mag fires.
So, this voltage appears at the key switch contacts and will cause an ionization of material, and can create a conductive path that can short the P-lead, or reduce the voltage spike, which will reduce the voltage at the spark plug.
This could show up as a ‘weak’ magneto, and cause an A&P to overhaul or replace the mag, when the problem is in the mag key switch.
So, a 10 – 20 year cleaning interval of the key switch contact block would be prudent.
Mine is about 30 yrs old, so I’ll be cleaning it next week.
Wow, this could explain a dual mag failure on an IO540, within 100 hours of full overhaul (mags, governor, and engine). And the NTSB could not determine the cause — which could have been the switch. If the pilot flying that Lance had had another 30 feet to stop, that plane would still be flying today. That pilot made a text book landing in a parking lot, only took the right nav light off going by a tree.