He has piloting experience, possible training and might even have a license.
And in the manga Alucard’s attitude is basically “fuck it we’ll steal a plane”, with no guarantee of Pip or Seras being able to pilot it, or being able to hijack a pilot.
He probably could very easily just the his ability to make humans do as he pleases via hypnosis. Just calmly pretending to be the pilot, that Seras and Pip are his crew.
But think about it
He was able to pilot the SR-71 Blackbird by himself, he knew all of it’s specs and understood the terminology, there was passion when he spoke about it.