What happened
On April 23, 2006, a Bell 206B-3 helicopter, registration PT-HQY, was performing an aeromedical mission near Anadian, Alagoas. The aircraft had departed from the Alagoas Military Police Academy to provide medical assistance to victims of a car accident on the AL-45 and was returning from the site.
While flying at approximately 500 feet above Lagoa Manguaba at 70 knots, the pilot noticed a loss of engine power and the activation of the LOW RPM warning light. The aircraft lost roughly 200 feet of altitude. In an attempt to compensate using the collective, the rate of descent increased. Unable to reach the shoreline, the pilot performed an autorotation and executed an emergency landing on the surface of the lagoon. All five occupants—the pilot and four passengers—were uninjured, though the aircraft sustained severe damage and remained submerged in saltwater for three days before being recovered.
The investigation
CENIPA investigators examined the engine, an Allison 250-C20B, and analyzed maintenance records. The investigation focused on the Fuel Control Unit (FCU) and its associated plumbing. Technical analysis by the IAE and Rolls-Royce do Brasil revealed that the engine was operating at low power during the landing.
Investigators discovered that the compressor pressure (PC) tube was connected to the FCU with only two threads of engagement, and the required locking device (safety wire/freno) was missing. This allowed air to leak from the connection. As the leak increased, the FCU received incorrect pressure information, leading the unit to reduce fuel flow because it incorrectly perceived the engine was approaching idle conditions. The investigation also noted that the aircraft's airworthiness and engine logbooks were outdated and that the pilot did not meet specific operational requirements for public security missions as defined by local authorities.