The Twin Commander’s high-wing configuration has many advantages—it affords great visibility for passengers; it contributes to a solid, heavy-airplane ride in turbulence; and it makes for a handy umbrella if you’re caught on the ramp in a surprise rain shower. The high wing also makes it much easier on the laundry bill to do the preflight inspection—no need to kneel on an oil-soaked tarmac to check the main landing gear.
About that preflight inspection—are you doing the squeeze play when you check the MLG? The squeeze play involves placing your thumb on one side of a MLG bungee cord and your forefinger on the other side and squeezing. If the two sides of the bungee touch, it’s time to replace it.
It’s important to do the squeeze play on every preflight inspection, for several reasons. First, the bungees live and work in a very harsh environment. They are fully exposed to wind and weather when the gear is extended. They are positioned just aft of the drains at the bottom of the engine nacelle, which means they get a regular dousing of fuel, engine oil, and hydraulic fluid. Those contaminants can cause sections of the bungee to swell, reducing their effectiveness.
Second, there is no calendar or time-in-service requirement mandating a formal shop inspection of the bungees. That means it’s up to the pilot to ensure the bungees are serviceable before every flight. And third, the bungees perform an important role in assisting in the main landing gear extension sequence, and in certain circumstances may be the only way to get the gear down and locked.
The bungees are made up hundreds of tightly bundled rubber bands covered with a synthetic weave that is color-coded to indicate date of manufacture. Each main landing gear has a pair of them, one on each side, looped between the main body of the gear and the drag brace. Their function is to assist gravity, the hydraulic actuator, and the nitrogen blow-down system to extend the main landing gear past the over-center point and into the down-and-locked position.
In the event of a hydraulic failure, the nitrogen bottle, with the help of the bungees, should fully extend the gear.
If you are having a really bad day and experience a failure of the hydraulic system and the nitrogen blow-down system, not to worry; the bungees are designed to step up and take charge. After slowing the airplane, select Gear Down and yaw the airplane side-to-side. Gravity will pull the main landing gear out of the wheel wells and the bungees should pull each gear leg past over-center and into the down-and-locked position.
When you hear the familiar “clunk” of the gear locking into place, thank the bungees—and give them a squeeze after you land.