Rockwell International S-2R N4977X accident near Oakley, California

Probable cause

An in-flight collision with an unmarked meteorological evaluation tower (MET) during an aerial application flight due to the pilot's failure to see and avoid the obstacle. Contributing to the accident was the lack of visual conspicuity of the MET and the lack of information available to the pilot about the MET before the flight.

NTSB analysis

The pilot was initiating an aerial application to a field when the airplane collided with a 198-foot-tall, unpainted metal meteorological evaluation tower (MET). No information about the MET was distributed in any Federal Aviation Administration (FAA) notices or other publications for pilots, and the MET was not equipped with any markings or obstruction lights for visual conspicuity. For these reasons, the pilot likely had limited opportunity to become aware of the MET before the flight, and his ability to detect it visually in flight was extremely limited. Although the pilot’s toxicological results were positive for dextromethorphan (an over-the-counter cough suppressant) and dextrorphan (a metabolite of dextromethorphan) in the urine, the substances were not noted in the blood; therefore, it is likely that some time had passed since the pilot had used the medication. Additionally, these substances would not normally be expected to result in any impairment.

METs are used to measure wind data throughout the United States. They can be assembled quickly and can be constructed of galvanized tubing with guy wires used as support. Because many METs (like the accident MET) are just below the 200-foot threshold at which FAA regulations would require the applicant to notify the FAA of the MET and to provide a lighting and marking plan for FAA assessment, many METs are unmarked, unlighted, and not referenced in any FAA notices or publications for pilots. Although the FAA in 2011 approved an update to Advisory Circular (AC) 70/7460-1K, Obstruction Marking and Lighting, that will provide recommended guidance on marking METs, ACs are only advisory in nature. Because of this, MET constructions will likely continue to meet only the minimum requirements and, thus, will remain a hazard to pilots operating at low altitudes. In March 2011, the NTSB published Safety Alert SA-016 to educate pilots about the flight-safety issues presented by METs. The Safety Alert is available at the NTSB’s website at http://www.ntsb.gov/safety/safety_alerts.html.

Text from the NTSB. Open the NTSB docket for WPR11LA094 for the full record.