Proficient Pilot

Precautionary landings

March 1, 1999

Although the investigation is far from complete, and conclusions cannot yet be drawn, the accident involving Swissair Flight 111 last September has attracted considerable speculation and Monday-morning quarterbacking. One criticism, for example, suggests that the crew might have reacted to the apparent electrical smoke and/or fire emergency and prevented the subsequent disaster by more expeditiously diverting to the nearest suitable airport.

It will be some time before the validity of this criticism can be determined, but the underlying philosophy can be used as a lesson to those of us who fly general aviation airplanes.

For the purpose of this discussion, landings fall into three categories. First is the normal landing. Next is the forced landing, when a pilot has no option other than to reconnect with Earth, usually because of total power loss. The precautionary landing is last. This is a premeditated landing — on or off an airport — when continued flight is possible but inadvisable.

According to this definition (which I confess is of my own making), lightplane pilots have an option that is not available to those who fly heavy iron. An off-airport landing often can be made safely in a small airplane but is not a viable option for those who fly jetliners.

There are innumerable occasions when a pilot might decide that a precautionary landing is safer than continued flight. The most obvious is when fuel is in critically short supply. Numerous pilots annually risk their lives and those of their passengers by not considering this option when uncertain of the amount of remaining fuel. Instead they overfly one safe haven after another (including airports) until their anxiety is answered with deafening silence. They fail to consider that a discretionary off-airport landing on a field of their choosing is far more preferable and safer than a forced landing without power.

The same strategy can serve as a valuable safety valve when in marginal weather conditions. According to the National Transportation Safety Board, "Any pilot who becomes trapped in weather and does not give serious thought to the feasibility of a precautionary landing on or off an airport [emphasis mine] often accepts the most dangerous alternative: continued flight."

There are, of course, many other circumstances that could justify a precautionary landing. These include:

  • Partial incapacitation of the pilot, especially when the condition is worsening.
  • Partial power loss.
  • Any worsening engine difficulty (in single-engine airplanes).
  • Serious airframe/powerplant vibration.
  • Impending nightfall when the pilot is untrained and the aircraft is inadequately equipped.
  • An oil leak of significant magnitude.
  • Structural damage such as a serious bird strike, a broken or cracked windshield, hail damage, strut failure, and so forth.
  • An indication of low oil pressure, excessive and uncorrectable cylinder-head temperatures, or abnormally low fuel pressure. (An alarming indication by a single gauge may be insufficient cause for emergency action unless there is an additional indication of abnormality; the problem could be a faulty instrument.)
  • Any worsening and threatening system difficulty (such as electrical fire and/or smoke) or flight control problem.

In other words, a precautionary landing is a viable option whenever continued flight is likely to become more hazardous. Unfortunately, it is seldom discussed during training because it is not a maneuver. Rather, it is a state of mind. It is a willingness to consider this alternative when conditions warrant.

Intentional off-airport landings are rare because pilots are not mentally prepared to use this option to escape worsening conditions. Many situations that justify such a strategy often develop into the drama of a forced landing (or worse) under more challenging circumstances because pilots are reluctant to correctly evaluate and acknowledge their status.

The flip side of this coin is that off-airport operations are not without hazard. They do impose a risk of damage and injury. A pilot who lands in a field, totals the airplane, and later learns that he did have enough fuel to reach his goal will be hard pressed for an explanation. On the other hand, he might not have had enough fuel.

So when is a precautionary landing advisable? There is no definitive answer; it is a judgment call. Consider, however, that a planned precautionary landing is almost always survivable, whereas the same cannot be said about forced landings, collisions with terrain, and untimely descents caused by other emergencies. It ultimately boils down to determining how much risk a pilot is willing to accept.

Opting for an off-airport landing isa difficult decision. But we must acknowledge that there are times when the alternative — continued flight — is potentially more dangerous. This is when a pilot should weigh the variables and decide upon a course of action that offers the greatest probability of survival before the passage of time and distance eclipse the option. Such a pilot is the captain of his fate, rather than the victim.