Aviation safety authorities in the United States and Europe warned pilots in April about potential risks flying in or near Ukraine airspace, where a Malaysian Airlines passenger airliner went down on Thursday.
The US Federal Aviation Administration on April 23 issued a "special notice" regarding Ukrainian airspace to US aviators and air carriers advising them not to fly in airspace around the Crimean city of Simferopol without special approval of the US government.
The notice also warned US operators and pilots flying in other parts of Ukraine, including Kiev, Lvov, Dnepropetrovsk and Odessa, to "exercise extreme caution due to the continuing potential for instability."
The warning remains in effect until April 23, 2015.
International aviation agencies in April also had warned pilots and airlines to avoid the airspace around Simferopol.
Agencies including the European Aviation Safety Agency and ICAO, a United Nations civil aviation agency, warned that airlines faced "serious risks" in the area and advised airlines to take alternate routes.