More common than you'd think as most crashes are on takeoff or landing, which tend to be in more built up areas.

We are discussing high altitude flyovers here.

Exceptionally unlikey a pilot would be able to crash a plane at 30,000 foot. Far more likely that a medical emergency would lead to a pilot landing at an unfamiliar airport and crashing the plane into block of houses.

Scenario: inexperienced/bad pilot misjudges fuel consumption (badly manages energy / height transitions) and requires emergency landing somewhere in EU because it cannot reach London