Avgas: Good to the last drop

February 1, 1993

Have you ever thought that you had a healthy fuel reserve on board and then later got a big surprise at the pumps? It's happened to most of us and can usually be attributed to the trip taking longer than expected, poor mixture management, or not starting out with full tanks. The result is the same-too close for comfort.

One Cessna P210 pilot cut his margins even closer. The pilot on an IFR flight to Greensboro, North Carolina, told controllers he was having "motor difficulty and needed to come straight in." He was given a vector direct to the airport but ended up short and was forced to land on a busy roadway. There was fuel remaining in the left tank, but the pilot had neglected to switch tanks.

In most cases when we end up with less fuel than anticipated, we have no one to blame except ourselves. Sometimes, however, an additional factor creeps in to complicate things. The AOPA Air Safety Foundation's Emil Buehler Center for Aviation Safety has just completed a review of the P210's safety record, and in studying, among other things, fuel mismanagement, some alarming facts came to light. P210 pilots exhausted the fuel almost twice as often as pilots of other turbocharged single-engine retractables. Even worse, fuel starvation accidents, where the pilot ran a tank dry while there was still fuel in another tank, occurred four times as often in P210s as the comparison group.

The comparison group consisted of the turbocharged Beech Bonanza, Cessna T210 and TR182, Mooney 231/252, and Piper Turbo Arrow, Turbo Saratoga, and Malibu. The T210, which has virtually the same engine and fuel system, had a similarly bad record. If the T210 were excluded from the comparison group, the disparity between the P210 and the other aircraft would be much greater.

In fact, fuel mishaps were the leading cause of accidents in P210s, totaling almost 29 percent from 1982 to 1988. Some of these were not of the "fender bender" variety either and resulted in severe or permanent inconvenience to the occupants.

Another experienced P210 pilot was low on fuel and diverted to an alternate but ran out of fuel on approach in IMC. A visual fuel check had not been performed, and although the pilot was intending to stop for fuel before heading on to the original destination, it wasn't soon enough.

Now this might all be chalked up to poor planning and decision-making, but the sheer numbers of accidents relative to comparable aircraft is puzzling. As the foundation researched this more, pieces of the puzzle began to fall into place. There has been some suspicion over the past few years that perhaps the usable fuel in the P210 isn't quite as much as stated in the pilot's operating handbook. This would indeed cause a shortfall in endurance.

According to the ASF review: "Cessna has tested the P210 on several occasions and concluded that the tanks would hold the published amount of usable fuel. However, unless the pilot has taken special precautions to ensure that the aircraft is level side to side and 4.5° nose up fore and aft, it is possible that the fuel load will be somewhere between 80 and 83 gallons on the P210N. [The POH indicates the P21ON can carry 90 gallons, 87 usable.] Under these conditions, the total endurance is estimated to be about 30 minutes less than shown in the POH."

The problem comes from having long, slender tanks and not much dihedral. Additionally, the location of the fuel filler port and the filler neck indicator, a metal collar that extends into the tank and shows reduced fuel load, conspire to make it difficult to top off the tanks. This happens when, one, the aircraft isn't quite level and an air bubble gets into the tank, or, two, the lineman doesn't wait for the fuel to diffuse into the tank from around the collar. The result is that the tank appears to be full when it may actually be several gallons short. Care in positioning the aircraft and patience in fueling will alleviate most of this, but the accident rate seems to prove that that's not how it's done in the hurried real world.

Cessna has properly become quite concerned. The following note, while it doesn't exactly confront the issue, appeared in the later model POHs: "Some indeterminate variables such as mixture leaning, technique, fuel metering characteristics, engine and propeller condition, and air turbulence may account for variations of 10% or more in range." A 10-percent shortfall on the P2ION equates to about 8 gallons (4 gallons per side) and, at normal cruise, would leave one high and quiet about 30 minutes early. Still, if you're down to half an hour until dry tanks, it's a flirtation with disaster. At 29 minutes, you violate the minimum fuel requirement for day VFR flight.

The FAA has just suspended an airworthiness directive that would have required the recalibration of the fuel gauges and a new filler cap and collar on 21Os. While the cap and collar are probably worthwhile investments because they allow fuel to flow more quickly into the tank and also reduce water contamination, calibrating the gauges does not really address the problem. The FAA suspended the AD because parts and test equipment are not available.

In most fuel-related 210 accidents, the gauges dutifully showed that the tank(s) were about to go dry, and the pilot ignored them. That shouldn't be a hanging offense because fuel gauges are notoriously inaccurate, and that's why you wear a watch.

Perhaps a better solution is to understand the fuel system and be conservative. Figure you've got about 80 gallons usable in a 210, and be sure to check the tanks visually. Keep a solid one-hour reserve, no matter what, and the problem is solved.

Complete copies of the P210 review are available for $19.95 through the ASF, telephone 800/638-3101.


See also the index of "Safety Pilot" articles, organized by subject. Bruce Landsberg is executive director of the AOPA Air Safety Foundation.