Interesting. I’d just assumed that the radar return would be easily able to distinguish a lear from a 777.
In light of the tinfoil theories the plane might be reused I find that tidbit disturbing. I’d thought it would be difficult for such a large plane to get close enough to a big metro w/o being busted by radar returns.
If the flight controllers aren’t using the returns in that way could a 777 could ‘lie’ as a learjet and get close to a major metro area?
A short tutorial, from a 35 year controller.
In aviation, there are two types of radar, 'primary' and 'secondary'. In today's civil environment, primary is seldom used, as it is unreliable and costly to maintain.
Primary radar is a display of transmitted energy that has been reflected back to the antenna. It appears as a 'blip' or 'blob', with some variation in brightness. It has no altitude information. A small target at short range would appear to be the same size as a large target at moderate range. Military radars are quite powerful primary radars, as only a kamakazi would fly into combat with a transponder.
Secondary radar consists of a ground transmitter sending a radio signal out, asking "hey, anybody out there?". The aircraft transponder receives the signal and replies with a four digit code and his altitude. The ground receiver then, via computer, displays the target on the display in the correct position, along with the altitude.
The aircraft transponder is also part of the collision avoidance system, but that is part of another tutorial.