Low clouds and restricted visibility prevailed as a Cessna 172 with three aboard began an ILS approach to Runway 18 at a Texas airport. The late-night instrument training flight was uneventful until the airplane entered a fog bank on approach.
The occupant who was observing the training of a commercial pilot by a flight instructor spotted runway lights to the left—not straight ahead where they belonged.
Later he told investigators that "during the approach the commercial pilot called out an altitude, possibly the decision height altitude, at which time the instructor pilot is said to have stated, 'Descend a little more,'" reported the National Transportation Safety Board on the resulting accident that killed the pilot flying. It added that after the pilots realized they were not aligned for landing, they improvised. "Rather than perform the previously issued missed approach procedures, one of the pilots decided to attempt a circle to land on runway 36."
After overshooting that runway, the airplane struck terrain while turning back to the south.
If you have ever felt that a voice—yours or someone else’s—is urging you to go lower on a close approach, keep such reports in mind. Unfortunately, finding them in the accident archives does not take much searching. The lack of proficiency and understanding of the safety-insurance they represent is a strong reminder to set high standards for your own proficiency work.
Do you always aim to fly to practical test standards on proficiency and practice flights? Are you sure?
It may feel like a PTS-based ride if you include a nonprecision approach, or a circling approach, in your routine. But don’t forget to review PTS fine print.
For example, for your circling approach, “The runway selected must be such that it requires at least a 90 degree change of direction, from the final approach course, to align the aircraft for landing,” says the Instrument Rating PTS.
As for altitude tolerances, you would be mostly correct to state that 100 feet of leeway is allowed at the authorized minimum descent altitude—but only on the upside. There’s zero tolerance for a downside error. And the flight path must permit "a normal landing on a runway."
What about your own tolerance for error? At any phase of the approach, don’t just sit there with a 100-foot altitude error because it’s permissible.
Fix it before it gets worse.