Strangely, this is one of the rare circumstances that it’s easier if it involves the military.
If it is a military aircraft that crashes onto your property, the area will be declared a National Defense Area until the incident has concluded and the wreckage is removed. I don’t know specifically who makes that declaration. A National Defense Area declaration has the same effect as turning the property into a military base, and the same rules as on a base then apply, including access. You won’t be getting into the area unless someone says it’s ok, and don’t expect them to say that. Usually, the military police have full jurisdiction over the scene. As engineer stated above, the government will be kind enough to replace what their hardware squished.
If it is a civilian aircraft, it can become more complicated. The fire department (and to a lesser extent, police) can enter your property without warrant under exigent circumstances. Can you think of another government agency, other than the fire department, that regularly, as a course of normal operations, enters private property without the owner’s permission or a warrant? The report of a fire or other emergency gives firefighters the full authority to enter private property for the purposes of preserving life and property. Investigation can begin during this time as well (see Michigan v. Tyler, 436 US 499 (1978) and Michigan v. Clifford, 464 US 287 (1984)). Once the incident is fully stabilized (which for an air carrier aircraft crash would likely be days), the exigent circumstances expire.
Each state has an aeronautics inspector of some type, that person is usually on scene of an accident within a few hours. The FAA is usually on scene within a few hours after the state inspector (or in some cases with or before). For an air carrier accident, NTSB would be establishing a major presence, and can take up to 12 hours to arrive. Thus, for the start of the investigation, we are still in the “exigent circumstances” phase, and no warrant is needed. We’re here, please step out of the way.
Once the incident is stable (a day or three?), as in the fires are out, the injured/deceased have been removed, and the fuel has been picked up, we enter a different phase. Now access to your property is questionable, and either your permission is needed, or if you don’t want to give permission, an administrative warrant is needed, or, if there is evidence of criminal activity, a search warrant. I don’t know if the NTSB has some sort of special powers granted to it under the compelling government interest theory that allows them to maintain a scene for a certain period. I can’t find it if there is, nor have I heard of anything either way in many conversations with a number of NTSB folks.
Cleanup of the site and removal of the aircraft is the responsibility of the aircraft owner/operator. If the local, state, or federal government steps in to remediate the site, they will chase the aircraft owner/operator (or their insurance company) to pay.
