As far as it taking a lucky shot, you must not shoot rifles much. A 12' diameter engine getting bigger and bigger in your scope as the jet rushed straight toward you down the runway would not present any difficulty. None at all, the shot could be made 10 out of 10 times.
If the "4 minute delay" (?) bothers you so much, (why?) why do you assume a bullet through an engine cannot cause a chain reaction, snipping a fuel line for example, which leads to a fire after a short delay?
As far as MY contacting an engineer etc bla bla bla, sorry, that's not how it works. I postit a hypothesis, YOU need to shoot it down and disprove it. You haven't come close.
I would envision the (hypothetical) runway sniper using a van soundproofed on the inside with cheap foam mattresses. The exact shooting position would be determined in advance so that a shooting chair and rifle rest could be set up inside the van in advance. The shot could be taken through a removed small rear door window. The shooter would drive to his pre-determined road side parking place, get in the chair, and use his 12 or 20 power off-the-shelf scope to observe the jets as they turned into the take off position. Seeing the big twin engine jet with the American Airlines logo, he would have plenty of time to settle in for his one and only shot.
As the jet races down the runway, he holds his crosshairs just above the center of the 12' engine. As the wheels come off the tarmac, he fires.
Even a .30 caliber slug through the engine turbines could cause the massive failure he seeks: even after 1, 2, 3 or 4 or 10 minutes. What does he care?
If the jet lands right on him, he screams "Allah Akbar" with a big grin on his face, and goes to collect his 72 virgins right away.
If the jet crashes beyond him or not at all, he gets back into his driver's seat, and checks his map for the route to Miami International, O'hare, Logan, or Dulles.
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So why do I go to the trouble of pitching this hypothesis? Because even if there was no sniper at the end of the runway at JFK today, there might be next week. The national guardsmen standing around looking scary in the terminals doing nothing but providing pseudo-security PR, should instead be patrolling the airport runway approaches with their M-16A2s, looking for my hypothetical but entirely possible (even likely) snipers.
What are they doing in the terminals anyway? Looking for hidden boxcutters with their X-ray eyes?
The only way to defend against this action is to get these people out of this country and keep them out. Even NG patrols can not prevent this action.