This Near Collision Between Two Airplanes Will Make Your Heart Skip a Beat

This seems like yet another boring refueling video taken by a KC-135 Stratotanker's flying boom operator—until the NATO E-3 Sentry AWACS plane almost crashes with it. At the last second, the Sentry's pilot pushes down in a massive negative G-force party, avoiding a fatal outcome. Things look fun when a major disaster is averted. [The Aviationist]

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DISCUSSION

As a former KC-135 and E-3 driver, I have been in situations like this from both ends. Typically, the tanker is on autopilot to provide the most stable platform. Of course the receiver aircraft is being flown manually. After a "contact" (connection) is made with the boom, the E-3 came in too close, causing the boom to exceed a preset mechanical safety limit and automatically disconnect. Because the E-3 came too close to the tail of the tanker, the pressure of the E-3's bow wave pushed the tanker's tail up. This caused the to tanker's nose to pitch down before the autopilot could correct for the increase in pressure from the E-3's bow wave (which is what we see in the video).

Large airplanes in close proximity have a definite and adverse effect on each other. The larger the receiver, the more the tanker autopilot has to fight the pressures from the bow wave the receiver creates. Often, when refueling a C-5 or E-4 (B-747), tanker pilots have to disconnect the autopilot and fly the KC-135 manually, because the autopilot often cannot handle the large and sometimes rapid changes in pressure on the tail.

When I flew the KC-135, I often practiced autopilot-off refueling just in case the autopilot failed, which was a common occurrence. To me it seemed to fail on check rides most often, which is why I practiced autopilot off whenever the receiver pilot would agree to it.

In this incident, I don't think either pilot necessarily did anything wrong. "Hitting" an inner limit, which is what happened here, often causes the tanker to pitch down. How well the autopilot (or tanker pilot, if flying manually) handles that change in pressure determines if it ends in the receiver just backing out for another try, or a breakaway (which is what happened here). What I did not like, though, was the boom operator not calling "Breakaway, Breakaway, Breakaway!", as required by regulations. He just said "Go, go, go, go!"