European members of the North Atlantic alliance are considering a plan that could see them deploy fighter jets in Ukrainian airspace to down Russian drones and missiles.

Sources familiar with the discussions told Al Jazeera that the proposal, dubbed “SkyShield,” would “put NATO planes and pilots into Ukrainian airspace for the first time, sending a powerful political message to Russia that Europe is committed to Ukraine’s defence.”

The plan was first reported in February. As many as 120 NATO aircraft could participate in the operations, which would be carried out by the members separately from the alliance. London and Kiev jointly worked up the designs for the mission. While it is intended to be implemented to enforce a future ceasefire, the sources said it would operate in combat conditions as well.

US forces will not participate in SkyShield, according to Al Jazeera, and it remains unclear which nations would take part should it go ahead.

The aircraft would be based in Poland and Romania and shoot down missiles along Ukraine’s Black Sea coast, which Kiev hopes would free up Ukrainian forces to focus on the front lines.

A commander in the Greek air force questioned the costs of the proposal and its chance for success. “We’d have to pay for people to be there, several shifts a day in all specialities … it will be exhausting,” Colonel Konstantinos Zikidis of the Hellenic Air Force told Al Jazeera. “On the other hand, the proposal downplays the effectiveness of air defence systems, which are very effective against cruise missiles and have a far lower hourly operating cost than aircraft.”

NATO members, led by the US, have sent multiple ground-based missile defense systems and several F-16s to Ukraine to help defend against missiles targeting its troops and cities. However, Ukrainian officials say they need significantly more air defense assistance.

Zikidis added, “It’s also not really the job of aircraft to hunt down cruise missiles. They can do it if they are given coordinates by air command. They can’t go out on flight patrol and spot them by chance. So you need a very thick radar array to cover a given area, especially at low altitude.”

The Greek military commander also expressed concern for the fallout if a Western aircraft were to go down while defending Ukraine. “If one European plane falls and a pilot is killed, it will be very difficult for a European government to explain it,” said Zikidis. “For a Greek pilot to go and get killed in Ukraine could bring the government down.”

Russian officials have warned throughout the conflict that any Western forces deployed to Ukraine will be considered a legitimate target.