Aviation Safety Letter 1/2003

Switchology

by Gerry Binnema, System Safety Specialist, Pacific Region, Transport Canada

Step into a modern airplane and what kind of cockpit layout will you find? The standard six instruments, the gear handle to the left of the throttle quadrant, the flaps to the right. The power controls will be in the standard order of throttle, prop and mixture. But this standard wasn't established overnight. Look into the cockpit of a 40s or 50s vintage aircraft and you could find any combination of locations for the various instruments and controls. Obviously, this lack of standardization created problems for people who went from one aircraft to another, so it was necessary for the manufacturers to agree on where to put what.

Although the standard cockpit layout is now quite predominant throughout the general aviation fleet, there are still many older aircraft that do not fit the standard. To make matters more confusing, some manufacturers switched from a non-standard layout, to a more standard layout in the middle of production of certain models. For instance, some Beech aircraft were manufactured with the gear handle on the right side of the power controls while later models had the controls on the left side. This means that stepping from one aircraft to another, even though they may be the same make and model, can bring some surprises.

The DHC-2 Beaver has a surprising reversal in its fuel selector control, one that is not mentioned in the Aircraft Flight Manual (AFM). The early models were built with a fuel selector with the "OFF" selection at the 12 o'clock position. This was modified at S/N 1313, to a fuel selector with the "OFF" selection at 6 o'clock, and the centre tank at 12 o'clock. 

Switchology (jpeg) Switchology (jpeg)

A modification kit (#2/1303) was offered for earlier aircraft. However, the AFM only illustrates the earlier, pre-mod fuel selector. Additionally, the throttle and propeller controls are also reversed between earlier and later production Beavers. Many operators have a fleet of Beavers with various combinations of fuel selectors and power control configurations, resulting in the potential for confusion.

These differences between aircraft are not generally a problem when a pilot is operating at a normal level of awareness and attentiveness. A brief glance at the control will be enough to confirm what the control is and what position it should be moved to. The problem comes when our attention is reduced due to a variety of human factors, or when our attention is distracted by other problems in the flying environment. This is when we start working from our old habits, and we will move a control the wrong way, or move the wrong control.

What is the solution? Obviously, we need to maintain a high level of awareness regarding the potential differences in the controls, but is there more that can be done? Some suggestions might include:

  1. enhance training on differences between aircraft, including the first symptoms that would occur when an incorrect selection is made;
  2. establish habits or procedures that would reduce the likelihood or severity of making a wrong selection at a critical time;
  3. establish a habit or procedure of looking at, touching, and saying out loud the name of the non-standard controls whenever using an aircraft with an unfamiliar layout;
  4. avoid flying aircraft that are likely to cause confusion; and
  5. modify all the aircraft in the fleet to the standard configuration.

The first three suggestions could be put into place with relative ease. The last two would require greater commitment, but may be something to establish as an objective for the long term. The most important aspect is to be aware of the problem and to take it seriously. A wrong selection can be made easily, and the results can be deadly.

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