Just some back of the envelope physics - Gravity would only slow the bullet slightly. Wind resistance makes more of an impact, but the bullet is still potentially traveling over 2000 ft/s if the shot was relatively direct (2500 feet straight up).
Specs
Fastest .50 BMG: 647 [grain] or 42 [grams], 3044 [ft/s] (928 [m/s]) out of a 45 [inch] (1.1 [m]) barrel. Acceleration due to gravity: -9.81 [m/s/s] 2500 [feet] = 762 [m]
Gravity
Position given original position, initial velocity, time, and acceleration (so we don't need to do calculus right now).
Assuming it goes straight up at the plane, which would give the highest possible velocity and energy.
x = x0 + v0 * t + 0.5 * a * t^2 x = 762[m] x0 = 0 v0 = 928 [m/s] a = -9.81 [m/s/s] (solve for t)
(Use Wolfram Alpha to solve the polynomial formula: 762 [meters] = 928 [meters per second] * t + 0.5 * -9.81 [meters per second per second] * t * t) (text input: 762 = 928 * t + 0.5 * -9.81 * Power[t,2]) t = 0.824716.
Velocity given initial velocity, acceleration, and time: v = v0 + a * t v = 928 [m/s] + -9.81 [m/s/s] * 0.824716 The bullet is still going 919 m/s without wind resistance at 2500 feet up assuming there's no air, but it goes fast, so there is quite a lot of air.
Wind resistance
Hornady estimates a .50 BMG that starts at 2950 [ft/s] will be going 2085 [ft/s] at 2500 [ft]. (https://riflebarrels.com/barrel-lengths-velocities-for-the-50-bmg/) This would be at standard temperature and pressure. In real life, there would be less wind resistance as the wind resistance decresases with altitude due to lower pressure.
It goes about 70% of the original speed assuming constant pressure.
Since gravity only slowed the bullet an inconsequential amount, we can work with a number that has a little bit less energy than this (round down for ease of math).
We can reasonably determine the bullet to be traveling more than 2000 [ft/s], or about 600 [meters/s].
Collision energy
E = 0.5 * m * v * v m = 0.042 [kg] v = 600 [meters / second] E = 7,560 [joules], or 5500 [ft*lbs].
That's still quite a lot of energy, and an ideal shot could have been more than that.
For comparison, per a quick Wikipedia check, a 45-70 at the muzzle puts out 3,449 [ftlbs] (4676 [J]). A 30-06 puts out 3036 [ftlbs] (4116 [J]).
The .50 BMG put more energy out at 2500 feet in the air, and makes a bigger hole. It would likely damage any aircraft. It may not immediately make the airframe unairworthy, but definitely damage would occur, especially if multiple shots hit.
Perhaps it's because of My Ding-a-Ling? https://m.youtube.com/watch?v=DMuTvoD1QNs
Someone pointed out... the finance guys (even the low level guys) won't tolerate it.
They're nary a vegan living in Broboken, NJ with all the fresh out of college IB guys... that shit wouldn't be tolerated even at the lowend.
Those facilities are closer to the Holland Tunnel, rather than the Lincoln Tunnel, as they wires use the routing of old Western Union telegraph lines. W.U.'s headquarters and ops center was at 60 Hudson Street, which was later purchased by AT&T (the original one) and used as their operation center. It's currently an enormous and well-connected internet exchange.
Buses from the Port Authority Bus Terminal enter and exit the Lincoln Tunnel on those ramps.
Dyer Avenue is the main entrance and exit between the streets and the tunnel itself, however the ramps from the PABT go directly into the tunnel.
Since the PABT is overcrowded, some buses pick up on the streets in the area, and drive into the tunnel so that's probably an accurate statement... people watch buses, trains and planes and it's a bit funny...
The bus terminal is owned and operated by the Port Authority of New York and New Jersey, a shared state agency across the two states that also operates the NYC area airports, and the PATH train service (Port Authority Trans-Hudson).
Cars can park inside the PABT (5th through 8th floors), and enter using the ramps as well. Unusually for NYC, it is a self-park parking facility, although it is far too large to have valet service.
Haven't heard that one in a while.
The requirement for a license to carry concealed in most situations that previously required it goes away on July 1st.
The licensing scheme will be retained primarily for reciprocity, but there are some edge cases as well.
I saw this more than 10 years ago in Seattle...
It was already bad there - we used to call one of the local McDonald's stores "McStabbies" - the homeless liked to stab each other in there.