Number 233
November 1998
Altimeter Settings Revisited
FL180 is the altitude at or above which all aircraft altimeters should be set at 29.92, and below which they should be set to the current barometric pressure of the nearest reporting station. A frequently reported cause for altimeter mis-setting incidents that occur during a climb or descent through this altitude is distraction by other cockpit tasks. In a report to ASRS from an air carrier Captain, distractions inside and outside the cockpit, including a mechanical malfunction, led to an altitude deviation: As our reporter noted, appropriate division of cockpit tasks (one pilot to fly the aircraft, the other to handle the malfunction), and adherence to procedures (the checklist) probably would have allowed the flight crew to catch this mistake before ATC did.
12 O’Clock High
An air carrier crew’s altitude problem started during preflight, when they failed to notice that their altimeter needles were aligned at the “12 o’clock” position–at an airport with a field elevation of 1,000 feet MSL. The First Officer reports:
s While descending through approximately 23,000 feet
and navigating an area of precipitation and thunderstorms, both air conditioning packs failed...As we worked on the pressurization problem...we were assigned 11,000 feet. As we leveled, ATC asked our altitude because he saw us at approximately 10,500 feet. Then we noticed that two of our altimeters were still set at 29.92 with the pressure at 29.42. Our workload was obviously heavy, but we should not have missed this basic procedure. Someone always must pay attention to flying. A 1997 ASRS study on flight crew monitoring incidents found that a large majority of such incidents occurred when the aircraft was in a “vertical” flight mode—climbing or descending. Flight crews also were more likely to experience monitoring errors while performing two or more flightrelated tasks—like the crew in this report who were avoiding weather, dealing with a pressurization problem, and talking to ATC, all while descending through FL180.
s After we leveled at 11,000 feet, Center said to descend
and maintain 11,000 feet. We replied that we were level at 11,000 feet. About a minute later, Center again said to descend and maintain 11,000 feet. They said they showed us level at 12,000 feet and pointed out traffic at 13,000 feet. About that time, we discovered that the altimeters were set to 28.88 instead of the proper setting of 29.88. We quickly descended to 11,000 feet. The night before, maintenance personnel had dialed both altimeters back to sea level…[the actual] field elevation is approximately 1,000 feet MSL. We accomplished all checklists on preflight, but failed to notice that the second digit [of the barometric setting indicator] had been set to an 8 instead of a 9. This is something that is easy to miss.
High to Low, Look Out Below
The rapidly changing weather associated with cold fronts and steep frontal slopes can create significant and sudden drops in barometric pressure, causing some pilots to mis-set their altimeters. An air carrier Captain provides an example: With winter around the corner, a related reminder applies: Flying into cold air has the same effect as flying into a low pressure area; that is, the aircraft is lower than the altimeter indicates. Altimeters cannot be corrected for temperature-related errors. However, pilots can adjust their minimum procedure altitudes to compensate for extremely low temperatures. Canadian pilots consult a government-provided chart to determine how much altitude to add to the procedure altitudes listed on approach charts, thus ensuring obstacle clearance during very low temperature operations. The U.S. Defense Mapping Agency publishes a similar altitude correction table for military pilots. Readers who would like more information about low temperature correction charts should refer to ASRS Directline, Issue #9, available on the ASRS Web site, at http://olias.arc.nasa.gov/asrs.
s During descent below FL180, I put 29.82 into my
altimeter. When the First Officer [FO] came back from talking to company on the #2 radio, he also put 29.82 into his altimeter. We were descending through 6,000 feet for 5,400 feet when the Approach Controller announced a ground proximity alert, and told us to climb immediately to 6,000 feet and to recheck our altimeters at 28.82. We started to climb, checked our altimeters and discovered our mistake… It was an unusually low altimeter setting that day. Both the FO and I wrote the correct altimeter setting on our note pads, and both of us misset the correct altimeter. Unusually low barometric pressures may take pilots by surprise, especially if the weather appears to be improving, leading the crew to believe that a higher altimeter setting looks plausible. The old adage, “High to low, look out below” is still sound advice. ASRS Recently Issued Alerts On...
Uncommanded autopilot disengagement on a DA-20 FK-100 fuel leak attributed to a dislodged fuel vent line Pilot confusion over control of stop-bar lights at a Florida airport Inadequate runway signs/markings reported at a Nevada airport Uncommanded reduction of B757-200 engine power to flight idle
A Monthly Safety Bulletin from The Office of the NASA Aviation Safety Reporting System, P.O. Box 189, Moffett Field, CA 94035-0189
http://olias.arc.nasa.gov/asrs
September 1998 Report Intake
Air Carrier/Air Taxi Pilots General Aviation Pilots Controllers Cabin/Mechanics/Military/Other 1680 697 59 198
TOTAL
2634
飞行翻译公司 www.aviation.cn 本文链接地址：美国ASRS安全公告CALLBACK cb_233.pdf
November 1998
Altimeter Settings Revisited
FL180 is the altitude at or above which all aircraft altimeters should be set at 29.92, and below which they should be set to the current barometric pressure of the nearest reporting station. A frequently reported cause for altimeter mis-setting incidents that occur during a climb or descent through this altitude is distraction by other cockpit tasks. In a report to ASRS from an air carrier Captain, distractions inside and outside the cockpit, including a mechanical malfunction, led to an altitude deviation: As our reporter noted, appropriate division of cockpit tasks (one pilot to fly the aircraft, the other to handle the malfunction), and adherence to procedures (the checklist) probably would have allowed the flight crew to catch this mistake before ATC did.
12 O’Clock High
An air carrier crew’s altitude problem started during preflight, when they failed to notice that their altimeter needles were aligned at the “12 o’clock” position–at an airport with a field elevation of 1,000 feet MSL. The First Officer reports:
s While descending through approximately 23,000 feet
and navigating an area of precipitation and thunderstorms, both air conditioning packs failed...As we worked on the pressurization problem...we were assigned 11,000 feet. As we leveled, ATC asked our altitude because he saw us at approximately 10,500 feet. Then we noticed that two of our altimeters were still set at 29.92 with the pressure at 29.42. Our workload was obviously heavy, but we should not have missed this basic procedure. Someone always must pay attention to flying. A 1997 ASRS study on flight crew monitoring incidents found that a large majority of such incidents occurred when the aircraft was in a “vertical” flight mode—climbing or descending. Flight crews also were more likely to experience monitoring errors while performing two or more flightrelated tasks—like the crew in this report who were avoiding weather, dealing with a pressurization problem, and talking to ATC, all while descending through FL180.
s After we leveled at 11,000 feet, Center said to descend
and maintain 11,000 feet. We replied that we were level at 11,000 feet. About a minute later, Center again said to descend and maintain 11,000 feet. They said they showed us level at 12,000 feet and pointed out traffic at 13,000 feet. About that time, we discovered that the altimeters were set to 28.88 instead of the proper setting of 29.88. We quickly descended to 11,000 feet. The night before, maintenance personnel had dialed both altimeters back to sea level…[the actual] field elevation is approximately 1,000 feet MSL. We accomplished all checklists on preflight, but failed to notice that the second digit [of the barometric setting indicator] had been set to an 8 instead of a 9. This is something that is easy to miss.
High to Low, Look Out Below
The rapidly changing weather associated with cold fronts and steep frontal slopes can create significant and sudden drops in barometric pressure, causing some pilots to mis-set their altimeters. An air carrier Captain provides an example: With winter around the corner, a related reminder applies: Flying into cold air has the same effect as flying into a low pressure area; that is, the aircraft is lower than the altimeter indicates. Altimeters cannot be corrected for temperature-related errors. However, pilots can adjust their minimum procedure altitudes to compensate for extremely low temperatures. Canadian pilots consult a government-provided chart to determine how much altitude to add to the procedure altitudes listed on approach charts, thus ensuring obstacle clearance during very low temperature operations. The U.S. Defense Mapping Agency publishes a similar altitude correction table for military pilots. Readers who would like more information about low temperature correction charts should refer to ASRS Directline, Issue #9, available on the ASRS Web site, at http://olias.arc.nasa.gov/asrs.
s During descent below FL180, I put 29.82 into my
altimeter. When the First Officer [FO] came back from talking to company on the #2 radio, he also put 29.82 into his altimeter. We were descending through 6,000 feet for 5,400 feet when the Approach Controller announced a ground proximity alert, and told us to climb immediately to 6,000 feet and to recheck our altimeters at 28.82. We started to climb, checked our altimeters and discovered our mistake… It was an unusually low altimeter setting that day. Both the FO and I wrote the correct altimeter setting on our note pads, and both of us misset the correct altimeter. Unusually low barometric pressures may take pilots by surprise, especially if the weather appears to be improving, leading the crew to believe that a higher altimeter setting looks plausible. The old adage, “High to low, look out below” is still sound advice. ASRS Recently Issued Alerts On...
Uncommanded autopilot disengagement on a DA-20 FK-100 fuel leak attributed to a dislodged fuel vent line Pilot confusion over control of stop-bar lights at a Florida airport Inadequate runway signs/markings reported at a Nevada airport Uncommanded reduction of B757-200 engine power to flight idle
A Monthly Safety Bulletin from The Office of the NASA Aviation Safety Reporting System, P.O. Box 189, Moffett Field, CA 94035-0189
http://olias.arc.nasa.gov/asrs
September 1998 Report Intake
Air Carrier/Air Taxi Pilots General Aviation Pilots Controllers Cabin/Mechanics/Military/Other 1680 697 59 198
TOTAL
2634
飞行翻译公司 www.aviation.cn 本文链接地址：美国ASRS安全公告CALLBACK cb_233.pdf
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