(Adds details about deaths in crashes and companies involved)
NEW YORK, May 1 (Reuters) - The U.S. agency that investigates airplane crashes urged the U.S. safety regulator on Thursday to audit several Alaska-based air carriers after a series of accidents over 19 months in which six people were killed.
In an urgent recommendation to the Federal Aviation Administration, the National Transportation Safety Board asked for a comprehensive audit of Era Aviation, Corvus Airlines, Hageland Aviation Services, Frontier Flying Service, Ravn Alaska and Ravn Connect, all owned by HoTH Inc. It also asked for an independent review of the FAA's oversight of the carriers.
Ravn Connect is the largest charter service operating in Alaska and was formerly known as Hageland, the NTSB said. It operates 1,200 flights a week with 58 airplanes.
The agency said evidence of "extensive" shortcomings in oversight and compliance call for an independent review of the companies and the FAA's oversight to ensure safety.
"We hope the FAA takes action," NTSB spokesman Eric Weiss said.
Officials from the carriers and HoTH were not immediately available to comment. The FAA said it had no immediate comment.
The NTSB cites six accidents and one incident by the carriers since September 2012, and four were in the last six months. A crash on April 8 killed two crew members and crash in November 2013 killed a pilot and three passengers.
After the November accident, the companies took action to try to reduce risk of crashes, the NTSB said. But a comprehensive review is needed to address "system deficiencies."
The planes involved are made by Bombardier, and by Cessna and Beechcraft, owned by Textron Inc. (Reporting by Alwyn Scott; Editing by Grant McCool)