Page 16 - Volume 21 Number 11

The Learjet 35 contains its fuel in two tip tanks, two wing tanks and an aft fuselage tank. The fueling process requires special care that one tip tank is not filled while the other remains empty.
up, and is normally done before landing or as the airplane taxis in.
After the line guys are done filling the tip and wing tanks, you absolutely must check each of the fuel caps for security. There is just one on each side, they look almost identical to those on a Cessna 310, lie on the outboard side of the tip tank and so cannot be seen from inside the airplane. If the left is less than fully fastened, they can depart the aircraft in flight, which will cause all the fuel on that side (literally a ton), to be completely siphoned out into the slipstream within a period of minutes. This in turn will cause the engine on that side to fail, and creates a lateral 2,400-pound fuel imbalance that makes the aircraft non-controllable around the horizontal axis. This “gotcha” is this reason you will find at least one of the pilots of a good Lear crew to be physically present during any fueling, and even after that, at least one of them will walk around the airplane and literally touch each of the two fuel caps before boarding. Personally, I check them twice.
Close the Door Already!
While still on the ground, the next “gotcha” with potentially fatal consequences is the cabin door closing mechanism. The complex process required to close the door has more steps than that needed to start the engines. Screw it up and a loss of pressurization could occur, which at the altitudes at which the airplane is capable of operating could easily prove fatal.
The process begins with pulling the lower half door up to a temporary lock
Despite all this fuel-thirsty, thoroughbred performance, and contrary to what you may have heard, Learjets are quite easy to fly. They have nicely balanced controls, go exactly where you point them, and have fighter-like acceleration and climb rates. It is hard to believe they were originally designed back in the early 1960s when most of us were still in high school or college. And yet, although the older models will do just about everything newer versions of the airplane will do, they have a reputation among pilots for some peculiar, mostly “age of design”-related operational issues, many of which can be fatal if you do not pay careful attention. In the vernacular of pilots, these become known as “gotcha’s.”
Avoiding the Gas Gaffe
Well before you board the aircraft, the Lear 35 “gotchas” start with the fuel system. The big TFE731 fanjets on these little airplanes each put out 3,500 pounds of thrust and use so much fuel that the engineers had trouble finding places to put it all. Just over 900 gallons can be boarded, and it is stashed all over the place. There is the equivalent of seven 50-gallon drums (1,175 pounds or 172 gallons on each side) in the wing tip tanks.
14 • TWIN & TURBINE
Inboard of each tip tank, squeezed into each of the small thin wings, there is another 1,254 pounds (a bit over 180 gallons a side). Finally, behind the baggage area aft of the rear passenger seat, there is a tank the size of a cattle watering trough called “the trunk,” which holds another 1,340 pounds or just under 200 gallons. The little jet, which has a basic operating weight of 10,700 pounds, takes off with just under 7,000 pounds of fuel on board.
With tanks scattered all over the airplane, filling them safely becomes a procedure that the pilots pay careful attention to. Unlike newer business jets, which nearly all have single-point refueling, the only way to fuel a Lear 35 is via the fuel ports in each tip tank where it flows by gravity into the wing tank on the same side. You must watch that the line guys do not fill up one tip tank while the other is empty, as that will cause a fuel imbalance of over half ton. Given the relatively narrowly spaced landing gear, this will tip the airplane literally up on its side. In addition, there is no way to place fuel into the fuselage or “trunk” tank from outside the aircraft. That tank can only be filled by transferring fuel from the wing and tip tanks via on board electric fuel pumps. It’s a time-consuming activity that usually requires the aircraft be powered
November 2017