Narrative:

Before departing; both student and I revisited the reported weather. The nature of the flight in question was instructional and centered around traffic pattern proficiency; thus terminal and local weather synopsis were sufficient for pre-flight review. Terminal cloud ceilings were textually reported at 1;500 feet AGL with scattered clouds existing around 300; ATIS broadcasting offered confirmation. With a warm occlusion powered by a maritime low to the south; I expected the cloud bases to gradually lower throughout the evening; however; no PIREPS were available to indicate any change to the current conditions. Departing runway 25; it is my understanding that a ceilometer exists just beyond the runway terminus; which dampened any concerns of encountering conditions other than reported during the initial climb. Pattern altitude established at 900 AGL; a determination was made to entertain the flight. Typically; any perceived anomaly in weather is relayed to the pilot during initial call-up. As none were addressed; I assumed none existed. With the student at the controls; we departed runway 25 as intended and began our initial climb in the upwind leg. At approximately 400 feet AGL (537 feet MSL); the aircraft entered hard IMC with no perceivable top. Visibility dropped to zero with no ground reference available. Knowing that the downtown structures loomed ahead; I immediately took control and executed a 90 degree left turn; reducing power to transition into a descent; during which merrill tower solicited a report of flight visibility. Break-out occurred at around 350 feet AGL over the quebec apron (south end of the airport) followed by an immediate landing on the departure runway. Though instrument proficient; inadvertent flight into IMC is by nature . . . Inadvertent. Therefore no planning was made leading to perceptual upset; further delaying the reactive process. The hazards involved are well-known and the possibility exists that future events may not yield favorable results. Though merrill has adequate weather reporting capability; field location is seasonally hampered by weather dynamics unique to the environment; leading to asymmetric field conditions. Tower/ground controllers are typically good about soliciting PIREPS from arriving traffic; but traffic must exist in the first place. I conclude that there was little that could be done to avoid this event based on the information available at the time. The reported weather conditions favored terminal flight well within my experience level and I believe my decision was justified on those grounds. Furthermore; the illusions associated with slant-range visibility and parallax make a visual ground estimation unreliable at best as the cloud ceilings looked adequate from my perspective. I would be hard-pressed to recommend additional technology as the requisite technology exists for data collection; though in this instance an anomaly may exist. However; due to the explained nature of merrill's environment; it may not be outside reason to employ the services of a trained human observer as such an anomaly could be fatal.

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Original NASA ASRS Text

Title: A flight instructor and student pilot experience unexpected IFR conditions on climbout when the reported weather and visual conditions indicated that VFR operations would exist.

Narrative: Before departing; both student and I revisited the reported weather. The nature of the flight in question was instructional and centered around traffic pattern proficiency; thus terminal and local weather synopsis were sufficient for pre-flight review. Terminal cloud ceilings were textually reported at 1;500 feet AGL with scattered clouds existing around 300; ATIS broadcasting offered confirmation. With a warm occlusion powered by a maritime low to the south; I expected the cloud bases to gradually lower throughout the evening; however; no PIREPS were available to indicate any change to the current conditions. Departing runway 25; it is my understanding that a ceilometer exists just beyond the runway terminus; which dampened any concerns of encountering conditions other than reported during the initial climb. Pattern altitude established at 900 AGL; a determination was made to entertain the flight. Typically; any perceived anomaly in weather is relayed to the pilot during initial call-up. As none were addressed; I assumed none existed. With the student at the controls; we departed runway 25 as intended and began our initial climb in the upwind leg. At approximately 400 feet AGL (537 feet MSL); the aircraft entered hard IMC with no perceivable top. Visibility dropped to zero with no ground reference available. Knowing that the downtown structures loomed ahead; I immediately took control and executed a 90 degree left turn; reducing power to transition into a descent; during which Merrill Tower solicited a report of flight visibility. Break-out occurred at around 350 feet AGL over the Quebec Apron (south end of the airport) followed by an immediate landing on the departure runway. Though instrument proficient; inadvertent flight into IMC is by nature . . . inadvertent. Therefore no planning was made leading to perceptual upset; further delaying the reactive process. The hazards involved are well-known and the possibility exists that future events may not yield favorable results. Though Merrill has adequate weather reporting capability; field location is seasonally hampered by weather dynamics unique to the environment; leading to asymmetric field conditions. Tower/ground controllers are typically good about soliciting PIREPS from arriving traffic; but traffic must exist in the first place. I conclude that there was little that could be done to avoid this event based on the information available at the time. The reported weather conditions favored terminal flight well within my experience level and I believe my decision was justified on those grounds. Furthermore; the illusions associated with slant-range visibility and parallax make a visual ground estimation unreliable at best as the cloud ceilings looked adequate from my perspective. I would be hard-pressed to recommend additional technology as the requisite technology exists for data collection; though in this instance an anomaly may exist. However; due to the explained nature of Merrill's environment; it may not be outside reason to employ the services of a trained human observer as such an anomaly could be fatal.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.