In 1945 a B-25 Mitchell bomber crashed into the side of the Empire State Building.
The accident didn't compromise the building's integrity but damaged floors 78 to 80.
However, fourteen deaths were recorded.
Damage estimated at $14 million in 2018.
On Saturday, July 28, 1945, Lieut. Col. William F. Smith Jr. was piloting a B-25 Mitchell bomber on a routine personnel transport mission from Bedford Army Air Field in Massachusetts to Newark Airport in New Jersey.
At 9:40 a.m., the aircraft crashed into the north side of the building carving an 18-by-20-foot (5.5 m × 6.1 m) hole where the offices of the National Catholic Welfare Council were located.
One engine shot through the Southside opposite the impact and flew as far as the next block, dropping 900 feet (270 m) and landing on the roof of a nearby building and starting a fire that destroyed a penthouse art studio.
The other engine and part of the landing gear plummeted down an elevator shaft.
The resulting fire was extinguished in 40 minutes. It is still the only significant fire at such a height to be brought under control.
Why the World Trade Centre didn't survive the hit and Empire State Building did? ✈️💥
WTC towers 1 and 2 were hit by Boeing 767 airliners travelling at around 500 MPH. At the time of impact, these aircraft weighed approximately 150 tons each and had an estimated 10,000 gallons of jet fuel on board that exploded on impact.
The Empire State Building was hit by a B-25 medium bomber. The aircraft was lost over New York in fog and was trying to land.
The B-25 probably weighed less than 15 tons at impact and was likely going under 200 MPH (320 km) at the time of impact. Fuel load at impact is unknown, however, it was coming in to land so was unlikely to be over 300 gallons.
The mass of the aircraft that hit the WTC was approximately 10 times as great.
The speed of the aircraft that hit the WTC was over twice that of the B-25.
That means the force of the impact on the WTC was over 20 times as great.
Fuel in the B-25 was approximately 3% that of the fuel on the 767s at impact.
Source: Wikipedia, Charles Fletcher (Quora)