Skyhawk 172/Cutlass 172
Air Traffic Control Fully Certified; Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument
Air Traffic Control Non Radar 25; Air Traffic Control Supervisory 4.5; Flight Crew Last 90 Days 15; Flight Crew Total 1050; Flight Crew Type 350
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR
Flight Crew Landed in Emergency Condition; Flight Crew Executed Go Around / Missed Approach; Flight Crew Diverted; General Maintenance Action
Aircraft; Procedure; Human Factors
I was too high [during approach] and did a go-around with the intention of flying straight out and returning. I applied full power but engine power started fading. I quickly did a check of carb heat (it was on); mixture was rich (full); fuel selector was on (both); primer (in); and ignition. I then re-attempted to apply full power; but power continued to fade. I glanced down and realized that turning around was not an option. I then looked ahead and noticed a straight stretch of highway about 1 mile ahead and headed for that. Luckily there were no vehicles present on the road. We made a safe landing on the road and pulled the airplane off the road. When we got out of the airplane we noticed fluid running from the bottom of the cowl. We determined it was fuel and quickly shut it off. The stream of fuel stopped. After pushing the aircraft off the road we removed the cowling to see if we could spot the problem. We turned the fuel back on and soon the fuel was running from the air filter box below the carburetor. It appeared as if the carburetor float had sunk or gotten stuck down and allowed fuel to freely flow through the carburetor and into the engine intake; probably flooding the engine and causing the power to fail. An investigation into the carburetor model (Marvel-Schebler MA4-5 10-3479) installed on the engine revealed that that carburetor was not approved for that engine (O-360). I had purchased this aircraft 2 months prior and had been flying it regularly. The aircraft was annualed in November of 2011. All AD's concerning the airframe; engine; and carburetor was signed off as being complied with. The aircraft had an STC for the O-360 engine and the paperwork for that appeared in order. The airframe had less than 2900 hours; did have previous damage history; but had thorough documentation of the repairs. The engine had only 85 hours since major overhaul. I had paid for and gotten a pre-buy inspection from an A&P recommended to me. A friend had recommended the aircraft as a good buy and had also made the A&P recommendation. Unfortunately I will not be able to trust either again for a recommendation. Upon removing the carburetor my A&P saw several discrepancies on the aircraft with just a casual glance. The EGT lead was attached to a primer line with a plastic tie. He moved the plastic tie to show how they rubbed together and showed an area where the primer line was starting to wear. The primer lines were installed using an automotive style compression fitting instead of the aircraft style which is soldered. The primer lines were loose in the fittings (I had not previously needed to use the primer and now I will not until they are replaced). The cylinder baffle springs were missing from all cylinders. An electrical line from the alternator to the firewall was of automotive quality. Upon removing the carburetor he showed me the fuel fitting going into the carburetor was incorrect and had crushed the fuel inlet screen. I took the carburetor to a carburetor specialist who tore down the carburetor and revealed additional problems. The 2 piece venturi that was subject to an AD (signed off during the 2011 annual as having been previously complied with) was epoxied in place so that it would not move (not an appropriate fix); the float was an old model black foam float that should have been replaced by a metal (brass) float or a new blue epoxy float. The float needle and seat were old (by age and design) and the mechanic showed that the needle was loose in the seat. The fuel nozzle in the venturi had been installed with a lock tab washer; however none of the tabs were pushed down to lock the nozzle in place. It could have come loose over time. An external bolt was in place with a serrated edge. It was installed with a lock tab washer instead of a serrated washer. Lock tabs are only of use with a hex head bolt. That bolt also could have come loose over time. In my estimation that carburetor was a ticking time bomb; negligently installed on this airplane by a [an unknown person]. It is a problem that probably should have been caught during an annual inspection. I am lucky that a safe off-field landing surface was available to me or the situation could have been much worse.
C172 pilot reports attempting a go around due to a high approach and finds the engine will only produce partial power. With the airport behind and unreachable the pilot elects to land on a highway. Upon shut down fuel is discovered draining from the engine cowl. Maintenance inspection of the engine reveals an unapproved carburetor along with fuel line and wiring components that are not suitable for aircraft use. The aircraft had been recently purchased and a pre purchase inspection was accomplished.