A helicopter accident in Arizona this week brings the death toll from crashes of medical helicopters and planes so far this year to 21, raising questions about the safety of medical aircraft, The Associated Press reports.

Tuesday’s crash of an Air Evac Lifeteam helicopter near Scotland, Ark., which killed three, was the fourth such fatal accident this summer.

This year’s total is up sharply from last year, when six people were killed. In 2004, the deadliest year for these accidents in the last decade, 31 people died in medical helicopter and plane crashes.

Robert Sumwalt, a member of the National Transportation Safety Board, told the AP that he is concerned that the Federal Aviation Administration has not implemented safety recommendations for the air medical industry made by his agency.

The recommendations include requiring helicopter operators to install systems that warn pilots when they are in danger of crashing into mountains or buildings and having formal evaluations to determine if flights are too risky.

An FAA spokesman said the agency plans to publish new safety rules soon.

There are about 800 airplanes and helicopters in the emergency medical transport industry.