Skyhawk 172/Cutlass 172
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 16; Flight Crew Total 818; Flight Crew Type 818
Situational Awareness
Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
Flight Crew Inflight Shutdown; Flight Crew Landed in Emergency Condition
Human Factors
Lost engine power possibly due to fuel exhaustion near the end of a VFR cross country flight. Landed safely on [a highway] without harm to the pilot and 3 passengers or people on the ground.The aircraft was fully fueled to 50 gallons before departing. After 3.5 hours to [destination]; the pilot had 24 gallons of 100 LL added at the FBO. Due to the aircraft being close to gross weight; it was not topped off. Total flight time that day was 7 hours with a total of 74 gallons available.The C172 has an STC that installed a Lycoming 180 hp engine. The pilot discussed with the owner the fuel consumption planning number as 8.1 gph and had seen that performance on previous flights of the aircraft; mostly solo flights. The STC paperwork was provided by the owner to the pilot for computing the weight and balance for the flights. The STC increases the max takeoff weight to 2550 pounds. The pilot loaded the STC weight and balance values into his Garmin Pilot app and used it to compute the weight and balance. The STC paperwork did not include changes to the aircraft endurance; climb; or other performance changes from an unmodified C172.The pilot used 8.1 GPH for planning the flights thinking that he had a total endurance of over 9 hours for both flights. Not completely knowing how the aircraft would perform with the maximum payload may have allowed the pilot to underestimate the fuel that would be consumed. Perhaps STCs should more fully describe any impacts to the aircraft performance.
C172 pilot reported landing safely on a highway after running out of fuel.