KENANSVILLE, FL, USA
N911HR
Mbb BO105CBS
While approaching a landing area to pick up a patient the pilot stated that as he passed through 300 feet, the helicopter began to descend rapidly. He applied collective control and engine power, but the helicopter continued to descend. The helicopter collided with trees and then rolled onto the right side, coming to rest in a swampy area. He did not observe any anomalies or warning lights. Post crash examination of the helicopter structure, flight controls, engines, driveshafts, and transmissions showed no evidence of precrash failure or malfunction.
HISTORY OF FLIGHT On September 10, 1999, about 0314 eastern daylight time, an MBB BO105CBS, N911HR, registered to and operated by Metro Aviation, Inc., as a Title 14 CFR Part 91 EMS positioning flight, crashed while approaching to land to pick up a patient. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter received substantial damage and the commercial-rated pilot and two medical attendants received serious injuries. The flight originated from Melbourne, Florida, the same day, about 0243. The pilot stated that at 0237, they were activated to respond to mile marker 210 on the Florida Turnpike to pick up an accident victim. They encountered some ground fog en route to the scene. They crossed the Florida Turnpike from east to west, about 7 miles north of the accident scene, at 1,000 feet. They could see the lights of the emergency vehicles. He descended to 700 feet and overflew the crash scene. About 300 feet above the ground, the helicopter began to descend. He applied collective control and engine power, but the helicopter continued to descend. The helicopter struck trees and rolled onto the right side, coming to rest. He did not observe any warning lights or notice any anomalies before the accident. PERSONNEL INFORMATION Information on the pilot is contained in this report under First Pilot Information, in Supplement U to this report, and in the attached NTSB 6120.1/2 Pilot/Operator Accident Report. AIRCRAFT INFORMATION Information on the aircraft is contained in this report under Aircraft Information and in the attached aircraft logbook records. METEOROLOGICAL INFORMATION Visual meteorological conditions prevailed at the time of the accident and winds were from the west-southwest at 3 knots. At the time of the accident the moon was at a bearing of 40 degrees at an altitude of -50 degrees, with 0 percent illumination. Additional meteorological information is contained in this report under Weather Information and in attachments to this report. WRECKAGE AND IMPACT INFORMATION The helicopter crashed about 500 feet west of the Florida Turnpike near mile marker 210. The crash site coordinates were 27 degrees 53.759 north latitude and 81 degrees 2.451 west longitude. Examination of the crash showed the helicopter was flying from west to east when it collided with trees while descending and rolled onto the right side, coming to rest. All components of the helicopter which are necessary for flight were located on or around the main wreckage. Examination of the flight control systems showed continuity of the flight controls in all axis. One rod in the forward and aft cyclic control system had failed as a result of impact damage. One rod in the collective control system had failed as a result of impact damage. The Nos. 1 and 2 engine drive shafts and the tailrotor drive shaft had twisting and separation consistent with rotation at the time of tree and ground impact. After the accident fuel was transferred from the main tank to the supply tank using the helicopters electrical system and fuel pumps. Fuel was then pumped from the helicopter through the Nos. 1 and 2 engine fuel lines. A total of 71 gallons of fuel was drained from the helicopter. The Nos. 1 and 2 engines had ingested debris into the compressor sections and debris was found in the turbine sections. After moving the compressor and turbine sections, they began to rotate freely. The Nos. 1 and 2 engine and accessories were removed from the helicopter and shipped to Rolls-Royce Allison engines, Indianapolis, Indiana. Under NTSB supervision the No. 1 engine was examined and then placed in a test cell. The engine was started and it operated normally to takeoff power prior to starting to torch through the exhaust. Post test examination of the compressor section showed it had sustained damage from ingestion of debris during the accident. The No. 2 engine was placed in the test cell and started. After reaching cruise power, the engine began to surge. The test was concluded. Post test examination of the compressor section showed it had sustained damage from ingestion of debris during the accident. MEDICAL AND PATHOLOGICAL INFORMATION The pilot, flight medic, and flight nurse received serious injuries as a result of the accident. The flight medic and flight nurse were wearing crash helmets at the time of the accident. The pilot was not wearing a crash helmet. Toxicology testing on specimens obtained from the pilot after the accident was performed by the FAA Toxicology and Accident Research Laboratory, Oklahoma City, Oklahoma. The tests were negative for carbon monoxide, cyanide, ethanol, and drugs. TEST AND RESEARCH Testing of fuel specimens removed from the helicopter after the accident showed the specimens met the requirements for Aviation Turbine Fuel and contained no contamination. (See attached fuel test report). The book Aerodynamics for Naval Aviators, issued by the U.S. Navy, Office of the Chief of Naval Operations, Aviation Training Division, as revised in January 1965, describes the helicopter flight condition "Power Settling", on pages 408, 410, and 411. The book states "True "power settling" occurs only when the helicopter rotor is operating in a rotary flow condition called the "vortex ring state." The flow through the rotor in the "vortex ring state" is upward near the center of the disc and downward in the outer portion, resulting in a condition of zero net thrust on the rotor. If the rotor thrust is zero, the helicopter is effectively free-falling and extremely high rates of descent can result." (See attached pages from the book). The book Flight Theory for Pilots, by Charles E. Dole, University of Southern California, states on page 153, "One of the most dangerous flight conditions that the helicopter pilot can encounter is known as settling with power or more technically known as the vortex ring state. In this condition the helicopter is descending into its own downwash. This can happen when the aircraft is making a vertical or near vertical descent with low forward speed." The book further states "The normal tendency to increase collective pitch while applying power is wrong. This action can aggravate the power settling." (See attached pages from the book). ADDITIONAL INFORMATION The aircraft wreckage was released to David Fry, Director of Operations, Metro Aviation, on September 11, 1999. The number 1 and number 2 engines, which were retained by NTSB for examination were released to Milton Geltz, Director of Maintenance, Metro Aviation, on October 13, 1999.
The pilots failure to recognize entry into settling with power during approach to land and his failure to take remedial action to escape from settling with power resulting in the helicopter descending and colliding with trees and swampy terrain.
Source: NTSB Aviation Accident Database
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