Because Jet Rescue Air Ambulance is a foreign company, the Philadelphia investigation could be a bit more challenging.

NTSB investigators have recovered the engines and cockpit voice recorder (CVR) of the Learjet 55 that crashed on Jan. 31 in Philadelphia, killing at least seven people.

The Learjet, carrying a pediatric patient and five others, crashed on Friday, killing all on board. On the ground, one person was killed and at least 19 others were injured, officials said.