Single-Pilot IFR Operations
Making landing approaches completely by instrument is a demanding piloting procedure. Pilots are given the instrument rating only after many hours of ground school, practice in flight, and rigorous ground and flight examinations. In the United States, nonairline instrument-rated pilots must renew their ratings every six months, either by an instrument competency check ride with a flight instructor or by having flown six hours under the hood or in instrument weather conditions, and also having made six instrument approaches in that time period.
Pilots of commercial airliners get a great deal more instrument flying practice than do private instrument-rated pilots. Private instrument-rated pilots must have a minimum of only six hours of blind-flying time and six instrument approaches every six months in order to remain current. Commercial airline pilots get frequent instrument flying practice because, by law, all airplanes operating above an altitude of 18,000 feet must be on an instrument flight plan. Also, jet air carriers have agreed with the FAA to fly under instrument flight plans when below 10,000 feet, although this is not required by law.
This attention to training is not misplaced, when one understands the cockpit environment in a personal airplane during an instrument approach in bad weather. The pilot has to cope with instrument readings of heading, lateral position, velocity, vertical position, and rate of sink, as a minimum. The pilot or pilots must also handle radioed instructions or advisories on headings, intersection crossing altitudes, radio frequency changes, traffic (other aircraft), wind, and airport runway conditions. Instructions, over a frequently busy and static-corrupted radio, must be repeated and copied on a knee pad as a backup to memory, since uplinked and displayed instructions are still in the future. Approach plates and landing checklists must be consulted under often poor lighting. Added to all of these may be concerns over icing conditions and fuel reserves.
By the time of NASA’s second flight test series on personal-airplane flying qualities, in 1966, personal airplanes were being used for precision ILS instrument approaches, often with a single pilot. It was and still is reasonable to ask whether the poor Dutch roll and phugoid damping, excessive longitudinal trim changes due to power application, and the badly designed trim systems found in the 1966 NASA tests add significantly to the singlepilot instrument approach problem.
Pilot workload studies in connection with instrument approaches began almost as soon as the procedures themselves. However, the few studies that examine the correlation between flying qualities and single-pilot instrument approach capability have not gone far enough. For example, a variable-stability airplane test at Princeton University used a single, experienced pilot, subjected to artificial distractions (Bar-Gill and Stengel, 1986). Only mild correlations were found between glide slope and airspeed errors and some stability and trim change parameters.
However, one would really like to know whether poor flying qualities can play a role in deteriorating a single-pilot instrument approach under more severe conditions and with less capable but instrument-rated pilots. Single-pilot instrument approaches under stressful conditions have ended in disaster many times, and we usually have no way of knowing what contribution was made by specific flying qualities.