Issue Number 246
December 1999
A Monthly Safety Bulletin from The Office of the NASA Aviation Safety Reporting System
P.O. Box 189, Moffett Field, CA 94035-0189

The Parallax Effect

The "parallax effect" describes a type of visual illusion in which the position of an object in 3-dimensional space appears to change, due to a shift in the position of the observer. The parallax effect can make distant fixed objects, such as a planet or star, appear to be close and in motion. The twinkling planet Venus is a well-known example in aviation. Tower controllers have often cleared Venus to land, while pilots have mistaken the planet for nearby aircraft position lights.

The parallax effect is especially apt to occur during night operations when there may be few, or no, visible references to the horizon as an aircraft moves through space. Several ASRS reports illustrate, beginning with a First Officer’s account of a nighttime evasive maneuver that startled crew and passengers:

A conservative approach, followed by the First Officer in this instance, is to avoid the perceived hazard first, and verify the nature of the hazard afterwards. Although this report didn’t mention crew fatigue as a factor, fatigue is known to be associated with susceptibility to the parallax illusion. U.S. Air Force research has shown that a few minutes of breathing 100% oxygen will help to refocus pilots’ thinking—and eyesight.

When To Their Wondering Eyes Should Appear

The parallax effect also can be experienced by several observers at the same time, as reported by a general aviation pilot who described a night flight with companions:

The reporter noted that contributors to the event were a very dark night with no moonlight, and the aircraft’s proximity to the ocean with its lack of surface lights and features. Awareness of the flight conditions conducive to the parallax effect can help keep pilots from falling victim to this illusion.

Ground Crew Safety Reprise

The August 1999 CALLBACK contained an article about a baggage handler who went to sleep in an airliner cargo hold and awoke at FL200. His banging in the cargo hold was heard by the cabin crew, and the aircraft made an emergency landing. But what happens when the cries for help of a cargo hold occupant can’t be heard? As this First Officer’s report concludes, the occupant may be lucky to survive:

Clip-on badges or flags of a distinctive color, attached to the cargo conveyer belt, would be an effective way of signaling that the cargo hold was occupied. Removal of the badges/flags could be a ground crew check item.

More on Battery Fire Hazard

An article in the October 1999 CALLBACK on battery fire hazard has created a ripple of interest, and several letters to the Editor. We’d like to share excerpts from this correspondence with readers who may carry spare batteries in their flight gear or personal belongings. We begin with a pilot’s tale of a battery explosion in flight:

Another reader adds a domestic note on battery-related "hot pockets" that has implications for many light-airplane pilots—and their passengers:

A summary of these battery care "life savers."

Where Not To Do a Run-Up

A general aviation pilot recently supplied ASRS with a compelling tale of "wrong way" ground navigation:

Tower controllers, as well as pilots of large jet aircraft, have a better overall view of runways and taxiways than do light airplane pilots. ATC should keep this in mind when giving taxi instructions. Pilots of light airplanes should ask for progressive taxi instructions when uncertain of directions.

ASRS Recently Issued Alerts On...
LR-25 dive attributed to autopilot malfunction
DME outage in a Central American circling approach
B-737 uncommanded roll during ILS coupled approach
Password protection for Terminal Doppler radar systems
B-727 loss of engine power after fuel crossfeed termination
October 1999 Report Intake
 Air Carrier/Air Taxi Pilots
 General Aviation Pilots