Cessna 150
Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument
Flight Crew Last 90 Days 150; Flight Crew Total 1275; Flight Crew Type 250
Situational Awareness; Time Pressure
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown; Inflight Event / Encounter Fuel Issue
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft; Human Factors
A student and I departed on a night cross country flight to ZZZ. We were at maximum gross weight with 16 gallons of fuel in our tanks. 3.5 gallons of fuel is unusable; meaning we had 12.5 usable gallons onboard. The 1-hour flight to ZZZ would take 1 hour; meaning we would have burned 6 gallons. Usable fuel remaining would be 6.5 gallons. A flight back to our home airport would take roughly 30 minutes; meaning we would only have 3.5 usable gallons remaining after we landed back home if we did not refuel. Therefore we knew we would need to re-fuel before heading home.My personal minimum is to have 1 hour of fuel remaining after each flight. The TAFs in our area were forecasting MVFR and IFR weather to arrive within 6 hours. This region is known for having bad weather arrive earlier than forecast. Therefore I wanted more than 1 hour of fuel to be in the tanks after we landed at our home airport so that we wouldn't be left without ample options to find a different place to land if the weather rolled in early.[By the time] we landed at ZZZ; both FBOs had closed. No self-serve fuel was available. Neither of us realized this until after we landed at ZZZ. Further complicating the matter is the fact that no airports on the way home had self-serve fuel. Rather than pay a fee for a line service after-hours call; we elected to go to a nearby airport to refuel. We chose ZZZ1; which had low-intensity runway lighting and self-serve fuel available; or so we thought. So we departed towards ZZZ1. The total enroute time was 20 minutes. We estimated we would have 4 usable gallons remaining. This was legal per actual fuel consumption numbers; but per a conservative burn rate estimate; it would have been below my personal minimums. I had not realized this until later when I would write this report.When we arrived over ZZZ1; we realized that the low-intensity runway lights were inoperative. This was an unexpected problem. Further complicating the matter is that this airport is located in essentially the middle of nowhere. I could see the beacon briefly illuminate portions of the pavement as it rotated around; but I could not take the chance at landing on a dark runway in unfamiliar territory. With 4 usable gallons remaining; we were now technically in emergency fuel status; but did not realize it at the time. We did know; however; that our fuel situation was getting uncomfortably tight.We had to make the decision to go back to ZZZ or choose another airport. We believed ZZZ would be slightly upwind and another airport to be slightly downwind based on our wind aloft estimations. The slightly downwind airport was ZZZ2; and it had self-serve fuel. The total time to ZZZ2 would be about 25 minutes. A conservative fuel burn estimate of 6 gallons/hour would mean we would use 3 gallons. In writing this report; I realize that would leave us with 1 usable gallon remaining. While actually flying the leg; I failed to account for the 'unusable' fuel and figured we would land with 5 gallons; failing to remember that 3.5 gallons of that would be unusable. I believe I was in denial about the whole situation.I notified the overlying approach control of the lighting situation at ZZZ1 and requested flight following to ZZZ2. The Approach Controller acknowledged my report and provided us with radar flight following to ZZZ2.Thankfully; all of our fuel calculation with a 20% more conservative burn rate than what is published in the POH. Despite knowing we had inflated the burn rate to be conservative; I was extremely nervous going into ZZZ2 because of the thought of exhausting all of our usable fuel. We made it to ZZZ2 without incident. When I exited the airplane; I used a dipstick to measure the fuel tank quantity. We had 2.5 gallons per tank for a total of 5 gallons remaining. 3.5 of those total gallons are unusable; meaning we had 1.5 gallons of usable fuel remaining. This was both illegal and below my personal minimums. I was horrified at what had happened.The chain of events went as follows: We depart at maximum gross weight with 16 gallons of fuel. We plan to arrive at an airport before the FBOs close; but land later than planned. Not wanting to pay an FBO call out fee; we depart for a nearby airport that has both runway lighting and self-serve fuel advertised in the Chart Supplement U.S. We arrive at the nearby airport with minimum fuel only to find the runway lighting inoperative. We make a decision to go to another airport that is downwind of the wind aloft and end up landing with 1 gallon of usable fuel; or 10 minutes of usable fuel remaining.This whole incident has resulted in a big change in approach to how I will conduct night cross country training in the future. First; our SOPs will be amended as follows:1. Flights to any airport must have an ETA of no later than 1 hour prior to the closing time of airport fuel vendors if the destination does not have self-serve fuel available.2. Night flights must have enough usable fuel onboard to reach two alternate airports; both of which must have fuel available and airfield lighting.3. In the event a flight lands at the planned destination and no fuel vendors or self-serve fuel are available; students are required to pay the call out fee to refuel. At night; the alternate airports may be flown to only if a call out is not possible.Next; I will be more involved in the cross country planning of my students. I should have recognized the fact that ZZZ had no fueling available well prior to arriving there after the FBOs had closed. And I should have required my student to pay a call out fee rather than agreeing to fly somewhere else considering that we didn't have legal fuel remaining to make it to an alternate should our refueling airport be closed; or in this case; should our refueling airport have an unexpected lighting outage.I reported the outage to the overlying approach control listed in this report. I then called FSS in the morning to report the outage. The Approach Controller seemed uninterested in the problem; and the FSS specialist referred me to the airport administration. When I called the airport administration; the manager was unavailable; and I was told to leave a message. To this day; 48 hours later; the problem has not been fixed; and no NOTAM has been issued.
Cessna 150 flight instructor reported departing with minimal fuel after founding that fuel was unavailable at the destination airport when the FBO closed.