Holes in the Cheese

Why would an airplane manned by five professional aviators (two pilots, three flight officers) fly directly into the water from 250 feet above the surface? That question vexed the aviation mishap investigation board (MIB), of which I was the flight surgeon member, for the two weeks following the E-2C Hawkeye mishap that I described in a prior post (http://www.mkmariner.blogspot.com/2012/02/mishap.html)

The E-2 executed a normal foul deck wave-off procedure from the aircraft carrier at night in marginal weather. As it climbed to 1/4 mile ahead of the ship, the Hawkeye nosed over and impacted the water at high speed. No one on board survived, nor were their bodies recovered.

A Navy aviation mishap board consists of five members. The board conducts a meticulous investigation of all factors that may have contributed to the mishap. The MIB does not assign blame, nor does it single out any individuals for disciplinary action. Its deliberations are held confidential, the sole raison d’etre being to identify correctable causal factors in hopes of preventing similar mishaps in the future.

One member of the board must be a designated naval flight surgeon. By virtue of our training in aviation medicine, and our direct familiarity with the aviation environment, we flight surgeons bring the tools and skill to identify human factors that may have been involved in the event. The board also looks for mechanical or structural issues with the airframe, training of air and ground crews, operational issues such as crew rest and readiness, and other factors.

Seldom does a single factor emerge as the sole cause. Most aviation mishaps — indeed most “accidents” in life — occur at the end of a chain of events, any one of which, if avoided, could have altered the outcome. A common analogy is that of Swiss cheese. If all the holes ever line up just right, the mouse can run straight through the cheese.

Our job on the MIB was to find the links in the chain, or holes in the cheese, that led to the tragic outcome. The evidence at hand consisted of the videotape that recorded the approach, waveoff, and descent of the aircraft (All carrier launches and landings are videotaped); assorted fragments of the aircraft, including a large chunk of the radome and several hundred other pieces no larger than a meter square; the crew’s service, aviation, training, and medical records; the aircraft’s maintenance records; and various other squadron documents. All that, and our collective expertise.

We found no suspect mechanical, operational, or training issues. The largest hole in the cheese came down to a human factor: spatial disorientation in an environment devoid of visual references. Several types of spatial disorientation exist, most of which involve either the visual or vestibular systems (eyes and inner ears). The specific condition that we believed initiated the mishap was the head-up somatogravic illusion:

Bodies in motion tend to head up or down with acceleration or deceleration. Think what happens if you put pedal to the metal in your automobile (We’ve all tried it at least once, right?). The front end lifts up. Conversely, tromp on the brakes, and the front end noses down. In the flight environment, the inner ear’s vestibular system acts like an accelerometer and interprets that sudden forward acceleration as an excessive head up motion, and sudden deceleration as an abrupt head down movement.

After four hours of flying oval patterns in a virtual milk bowl, the E-2 broke out of the overcast and made a normal descent to landing on the carrier’s deck. Just as it came over the ramp it was waved off for another aircraft still in the landing area. Per procedure, the pilot immediately applied full power and started a climb back toward the black night and the cloudy goo. We reasoned that the acceleration into total darkness caused the pilot to believe the nose of the aircraft was rising too fast, risking a stall. He pushed the yoke forward to compensate, and flew the airplane into the water.

“Yeah, DoK, but…”

Indeed, the explanation generated more questions than answers. There had to be more holes in that cheese. What were the other four crewmembers doing? The co-pilot could have grabbed the controls. The flight officers in the back could have raised an alarm. Why would they all sit there, unless they were distracted by something else? What?

And why would a seasoned aviator succumb to an illusion for which he’d been trained and experienced? Perhaps fatigue? We questioned the leadership judgment of conducting night flight operations in bad weather at the end of a long day following a difficult trans-Atlantic passage. Was the mission flown worth the lives of five men?

We could not prove our theory. The only ones who could say what happened in the aircraft that night did not survive to tell their stories. At the very least, we felt we succeeded in finding most of the holes in the cheese, and raised awareness of these human factors for future training — to possibly avert similar events in the future.

For the five men who died that night, it was perhaps a legacy.