Also I NEVER leave my keys in my car.
Maybe it's because I am from NY.
whenever I see it I am always like wtf are these people doing leaving their car with keys in it? LMAO

 

I was born and raised in San Francisco, CA... One of the hilliest major cities in the world. I always park an automatic car by setting the parking brake before putting the car in park and removing my foot from the brake, as well as turn/curb the wheels appropriately. I also park my manual cars with the parking brake and in gear with the wheels turned appropriately for the grade.

The parking pawl can fail with the full weight of the car, and once it starts rolling the pawl will, more likely, not be able to stop the car; like slamming a moving car into park all you will hear is the parking pawl grinding/popping.

Sorry about your car and the damage to the building.

 

No Brakes because I yanked door open while running full speed and did a head first swan dive into car with arms extended toward gearshifter. No way to jump in and sit or pull parking brake up, I was laying prone accross seat on top of parking brake. That was my only shot at stopping it.
(My Ribs, Knees, forarms and elbows took a beating...bruises and cuts but minor.)

When I got my wits about me and looked, the car was indeed in Park. So it was either in park at top of hill or 2/3rds of the way down the hill after I dove in it. Regardless, it rolled a good 15 feet in park, with no visible skid/slide/lockup of either rear tire.

Estimate for car repair-abour $2200...Building unknown-I would guess 5K.

And No, generally I don't use parking brake accept on very steep hills, this was not that steep. And I did leave keys in because I was out on acreage in a private place, in a place where theaft was highly unlikely. Ussually keys are in my pocket.

It does not matter which way the wheels were turned-it would of hit something.(Truck boat, tree or building.) It followed the angle the wheels were turned. Picture a counterclockwise circular driveway on a hill. I got to the top and sort of flattened out the turn in front of the house-that set the streering angle a little loser than the diameter of the circle-causing the car to track off the driveway into the building.

 

If you were close enough to the gear shifter to throw it in park, why not just grab the parking brake and give it a good yank up?

 

Wow, there are some rude people in this thread! Sorry about your car OP. To answer your original questions, I've never heard of a park interlock failure on Mustangs before.