Out of fear that Hamas forces in Gaza have obtained anti-aircraft missiles, the Israel Air Force now only operates helicopters equipped with anti-missile defenses over the Strip. As an additional precaution, the aircraft hover over Gaza at a significant, undisclosed, altitude. "We always assume the worst-case scenario," explained a senior IDF officer. "We assume they have the capability, even if we don't know for sure that they have it." The officer mentioned the attack on the INS Hanit missile ship during the Second Lebanon War. The IDF had not been certain that Hizbullah had obtained advanced shore-to-sea missiles like the Chinese-made C-802 with which it struck the ship. "Now, no one is taking any chances," the officer explained, adding that a large percentage of the IDF's reconnaissance operations over Gaza were conducted using unmanned aerial vehicles (UAVs). On Thursday, a helicopter was almost hit by what appeared to be a projectile fired from Gaza. OC IAF Maj.-Gen. Elazar Shkedy has assembled a team of aviation and missile experts to study the incident and try to determine whether there was a projectile - and if so, what exactly it was. Officials said the helicopter pilots had not noticed anything out of the ordinary, but televised footage of the incident showed a trail of smoke passing fairly close to a helicopter that participated in IDF operations in Gaza on Thursday. Meanwhile Sunday, IDF troops shot and killed two Palestinian gunmen trying to plant an explosive device next to the border fence in the southern Gaza Strip. The soldiers spotted the two near the Kerem Shalom crossing, opened fire and killed them. The IDF later sent soldiers into Gaza to search the bodies of the gunmen, who were carrying automatic rifles in addition to the explosive device.