united-states, under the Federal government's Special Maritime and Territorial Jurisdiction, such as in a US-registered aircraft over the high seas:
The pilot is guilty of, at least, common-law assault. (I cannot find a Federal definition of assault, so AFAIK that means the common-law definition is used.) Assault is "the wrong act of causing someone to reasonably fear imminent harm." (Please correct this if there is a Federal definition of assault, but I'm sure the pilot's actions are still in violation of any such definition.)
"Murder is the unlawful killing of a human being with malice aforethought," according to 18 USC § 1111(a). Because the pilot's intent is to commit murder, he is guilty of assault with intent to commit murder, and can be sentenced to up to 20 years in prison under 18 USC § 113(a)(1).
If the pilot does kill someone, this is murder. Because it is "willful, deliberate, malicious, and premeditated," it is first degree murder under 18 USC § 1111(a). In Special Maritime and Territorial Jurisdiction, the pilot can be sentenced to death or to life in prison under 18 USC § 1111(b).
The pilot's actions may be aircraft piracy. According to 49 USC § 46502(a)(1)(A), "'aircraft piracy' means seizing or exercising control of an aircraft in the special aircraft jurisdiction of the United States by force, violence, threat of force or violence, or any form of intimidation, and with wrongful intent." The pilot is exercising control of the aircraft, is doing so with wrongful intent, is likely using force in order to prevent the passenger from taking control. According to 49 USC § 46502(a)(2), the pilot is subject to imprisonment for at least 20 years if everyone survives, or death or life imprisonment if anyone dies.