Safety Publications/Articles

Breaking The Accident Chain

In our training, we have all heard of the infamous accident chain and the connecting links that ultimately lead to an aircraft accident. If at any point leading up to the accident a link is broken by a sound decision, the accident is prevented. Recently I have been analyzing a number of aircraft accident cases from the NTSB database. The links of an accident chain stand out dramatically in every case I examined. When teaching students aeronautical decision making, flight instructors should emphasize the importance of the accident chain in preventing accidents.

Consider this recent case. A student pilot with 1.7 hours of dual night experience flew a Cessna 150, solo, 48 nm from his home base to another airport so that he could meet an instructor and fulfill his night cross-country requirement. It was still daylight when he landed. The instructor found him totally unprepared and tired, but anxious to get the night cross-country out of the way. The instructor spent a considerable amount of time with him to prepare for the flight but was hurried because it was getting late. The instructor calculated from the pilot's operating handbook that, considering the flight time from the home base and the three legs involved in the cross-country, there would be enough fuel with a 45-minute reserve to complete the mission. He elected not to refuel.

After dark the flight began. Shortly before reaching the first airport, the generator warning light illuminated. The student told the instructor, "it happens all the time. It's a bad light." There was no ammeter installed in the airplane to confirm the faulty indication. They did a touch and go at this airport and proceeded on the second leg. During the approach to the next airport, the instructor had a problem activating the pilot-controlled lighting with the radio, but he dismissed it as not being close enough to the airport. After finally getting the runway lights on they executed a touch and go and began the third leg back to the airport where the cross-country flight originated. The generator light remained illuminated.

During the last leg of the flight the instructor noted that the gas gauges were showing almost empty. It is at that point the student told the instructor that the Continental O-200 in this airplane burned more fuel per hour than indicated in the POH. Neither realized that the fuel gauges on this airplane were electrically driven and that a power failure will cause the gauges to show empty. Needless to say, this added a lot more stress and anxiety to the flight.

Upon arriving at the airport at 10:40 p.m., the instructor was unable to activate the runway lights with the radio. By now the cockpit lights, landing light, radio, and flaps had all failed because of the generator problem. The instructor located the rotating beacon on the field and had identified the runway orientation. On short final, the student turned on a flashlight to examine one of the instruments, momentarily blinding the instructor. The airplane bounced several times along the side of the runway and ended up in a ditch, killing the student and seriously injuring the instructor. This 1965-model airplane did not have shoulder harnesses.

In hindsight, this instructional flight was a disaster from the beginning. Let's look at the links in the accident chain:

  1. The student flew 48 nm from his home to the lesson and was tired and unprepared. Break the link by sending him home to fly his cross-country another day. (It is not known from the accident report whether the student pilot had the proper training and endorsements for repeated solo flights to airports fewer than 50 nm from the base airport.)
  2. The instructor was not familiar with the aircraft's quirks, such as ongoing generator problems and abnormal fuel burn. Break the link by having full knowledge of the airplane and not flying until the airplane is adequately repaired. The lack of an ammeter while flying at night should cause concern.
  3. The generator warning light was ignored. Break the link by landing after the first leg and checking it out.
  4. The instructor had trouble getting the runway lights to activate at the second airport. Break the link by realizing that too many things are now beginning to go wrong. It's time to get on the ground.
  5. The student and instructor thought the airplane was running out of fuel because they did not realize that the gas gauges are electrical. This added to the stress of getting the airplane on the ground as soon as possible at the end of the final leg. Break the link by knowing how airplane systems work.
  6. The student was not aware that turning on a flashlight would destroy night vision. Break the link by ensuring students understand all aspects of night flying, including the characteristics of night vision, during their night proficiency briefing.

There were six links in this accident chain. Breaking any one of them before or during the flight would likely have prevented the accident. The lesson here is to teach your students to recognize when the links are beginning to develop and do something about them. It's a time-tested method to prevent tragic accidents like the one we discussed.

Richard Hiner is vice president of training for the AOPA Air Safety Foundation.

By Richard Hiner

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