Number 246
December 1999
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: same direction and was now much closer. After another brief moment, we realized that what we were looking at was the landing lights of two separate aircraft approaching from the west and that we were experiencing a visual illusion. It was not until the aircraft finally got close enough to see the position lights that we were able to distinguish one aircraft from the other… 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.
I I observed what I believed to be an imminent traffic
conflict. I manually overrode the autopilot and started an immediate left turn. The perceived conflict was a result of slight parallax of green and red wingtip lights of another aircraft. A bright white star also appeared as one of the running lights on the perceived conflict. The maneuver was a gut reaction on my part, as I perceived the aircraft to be within a few thousand feet from us. Passengers and flight attendants who were not seated with their belts fastened were upended in the cabin. One passenger received an abrasion to a knee and one complained of a neck injury… After landing…[no passengers] required medical attention… The aircraft was inspected for overstress and no discrepancies were found. 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.
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:
I I was the First Officer on a cargo/mail flight from XXA
to XXC, with a 16-minute stop in XXB. The first leg was flown at FL310 and the second leg at FL270. During postflight duties at XXC, our company mechanic came to the cockpit and advised there was a foreign national in our aircraft cargo compartment, cold but alive, stating that he was a company employee that had been closed in the aircraft belly compartment in XXA. Maintenance also advised the airport security and an ambulance were enroute.. The man appeared cold but otherwise OK. He said he was waiting in the aft belly for cargo to be loaded. No cargo arrived. The door was closed. Due to the ramp noise, hearing protection, and the APU I can only assume no one could hear his cries and knocking for attention. It is the responsibility of the loading crew to look inside the compartment before closing the door… It is my understanding that my company and the FAA are looking into ways to prevent this from happening again… If this had been a much longer flight, I am sure it could have been fatal. As it was, the man was closed in the compartment for a total of 2-1/2 hours; 1/2 of that [time] was in flight. 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.
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:
I There were 3 of us in the cockpit, including 1 non-pilot.
We were heading northbound over the peninsula… All 3 of us looked off to the 9 o’clock position and saw 2 landing lights which appeared to be a single large aircraft approaching at a very rapid rate… We banked to the right and pulled the throttle to idle in an attempt to avoid what appeared to be an imminent collision course. We then returned to level flight to see that the perceived aircraft was still approaching from the
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
A Monthly Safety Bulletin from
The Office of the NASA Aviation Safety Reporting System, P.O. Box 189, Moffett Field, CA 94035-0189
October 1999 Report Intake
Air Carrier / Air Taxi Pilots General Aviation Pilots Controllers Cabin/Mechanics/Military/Other TOTAL 1912 675 69 100 2756
B-727 loss of engine power after fuel crossfeed termination http://olias.arc.nasa.gov/asrs
飞行翻译公司 www.aviation.cn 本文链接地址：美国ASRS安全公告CALLBACK cb_246.pdf
December 1999
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: same direction and was now much closer. After another brief moment, we realized that what we were looking at was the landing lights of two separate aircraft approaching from the west and that we were experiencing a visual illusion. It was not until the aircraft finally got close enough to see the position lights that we were able to distinguish one aircraft from the other… 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.
I I observed what I believed to be an imminent traffic
conflict. I manually overrode the autopilot and started an immediate left turn. The perceived conflict was a result of slight parallax of green and red wingtip lights of another aircraft. A bright white star also appeared as one of the running lights on the perceived conflict. The maneuver was a gut reaction on my part, as I perceived the aircraft to be within a few thousand feet from us. Passengers and flight attendants who were not seated with their belts fastened were upended in the cabin. One passenger received an abrasion to a knee and one complained of a neck injury… After landing…[no passengers] required medical attention… The aircraft was inspected for overstress and no discrepancies were found. 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.
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:
I I was the First Officer on a cargo/mail flight from XXA
to XXC, with a 16-minute stop in XXB. The first leg was flown at FL310 and the second leg at FL270. During postflight duties at XXC, our company mechanic came to the cockpit and advised there was a foreign national in our aircraft cargo compartment, cold but alive, stating that he was a company employee that had been closed in the aircraft belly compartment in XXA. Maintenance also advised the airport security and an ambulance were enroute.. The man appeared cold but otherwise OK. He said he was waiting in the aft belly for cargo to be loaded. No cargo arrived. The door was closed. Due to the ramp noise, hearing protection, and the APU I can only assume no one could hear his cries and knocking for attention. It is the responsibility of the loading crew to look inside the compartment before closing the door… It is my understanding that my company and the FAA are looking into ways to prevent this from happening again… If this had been a much longer flight, I am sure it could have been fatal. As it was, the man was closed in the compartment for a total of 2-1/2 hours; 1/2 of that [time] was in flight. 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.
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:
I There were 3 of us in the cockpit, including 1 non-pilot.
We were heading northbound over the peninsula… All 3 of us looked off to the 9 o’clock position and saw 2 landing lights which appeared to be a single large aircraft approaching at a very rapid rate… We banked to the right and pulled the throttle to idle in an attempt to avoid what appeared to be an imminent collision course. We then returned to level flight to see that the perceived aircraft was still approaching from the
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
A Monthly Safety Bulletin from
The Office of the NASA Aviation Safety Reporting System, P.O. Box 189, Moffett Field, CA 94035-0189
October 1999 Report Intake
Air Carrier / Air Taxi Pilots General Aviation Pilots Controllers Cabin/Mechanics/Military/Other TOTAL 1912 675 69 100 2756
B-727 loss of engine power after fuel crossfeed termination http://olias.arc.nasa.gov/asrs
飞行翻译公司 www.aviation.cn 本文链接地址：美国ASRS安全公告CALLBACK cb_246.pdf
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