[Lonesome in Massachussets]

[O]fficial said it would be "extra-ordinarily difficult" for a light plane to crash into a large passenger plane due to collision avoidance systems in larger airliners.

Not if the small aircraft turns off his transponder, which is the only way automated collision avoidance system can sense another aircraft. At many airports (e.g., Heathrow) ground controllers turn off the "primary" radar display and depend entirely on "secondary" or tranponder echoes. The 9-11 hijackers turned off the transponders.

Steering a collision course isn't that hard, all you do is "null the line of sight rate", which is easier than it sounds.

If you miss you can always try again on the next arrival.

[MoralSense]

[O]fficial said it would be "extra-ordinarily difficult" for a light plane to crash into a large passenger plane due to collision avoidance systems in larger airliners.

Not if the small aircraft turns off his transponder, which is the only way automated collision avoidance system can sense another aircraft.

Also not if the airliner is on the ground, standing in line with a bunch of other loaded airliners on a taxiway.

[Kozak]

Steering a collision course isn't that hard, all you do is "null the line of sight rate", which is easier than it sounds.

Yup, steer till the object is at a constant spot on the windscreen, and bingo, collision course.

[kingu]

The official in question had no idea what they were talking about. If the target is on the ground, what the hell is a collision avoidance system going to do? Make the plane bounce into the air?

There's been enough accidents over the years to know that yes, you can fly a small plane into a jumbo jet if the jet is on the ground. In the air, much harder.