Pilots of commercial airlines that fly into Israel are expressing increased opposition to a security program imposed by the country’s Ministry of Transport that they say could subject inbound flights to possible attack by Israeli warplanes.

Last week, an Ethiopian Airlines Boeing 737 flight to Tel Aviv was intercepted as it approached Israeli airspace when pilots failed to correctly submit a code confirming their identity as required under the security program. The plane was prohibited from landing until it was determined not to be a security threat.

"People were scared; we didn’t know what was going on,” one passenger on the plane was quoted by Israeli newspapers as saying.

The incident was at least the second since the security program began its trial phase last year. It has brought out into the open a debate that has been ongoing in the international aviation community over the program, which was designed exclusively by and for Israel as a security measure.

Commercial pilots, including Israelis, say it creates logistical problems and safety hazards without improving security.

“It raises a serious possibility that in an extreme case, use of the system could bring about the shooting down of an innocent plane and its passengers,” said the president of Israel’s pilots union, Capt. Boaz Hativa.

The security program requires the pilot to carry an Israeli-supplied card with a personal PIN that must be submitted electronically before entering Israeli airspace. Clearance to land is dependent on the input of the correct code.

In April 2009, an incoming Delta Air Lines flight triggered an alert and an Israel fighter jet was scrambled to intercept. “The aircraft was determined to be a threat, placed in a holding pattern,” according to a letter written by Delta’s managing director of corporate security, Randy L. Harrison, to the Ministry of Transport. A copy of the letter was obtained by The New York Times.

While the plane was eventually escorted into Tel Aviv by the Israeli fighter jet, Mr. Harrison complained that “the subsequent investigation into the failure was never released to Delta and Delta was never informed of what corrective measures were implemented to prevent recurrence.”

Susan Elliott, a spokeswoman for Delta, said the letter was written to encourage the Israelis to work out these problems with the International Air Transport Association, a trade group representing 230 airlines. Steve Lott, spokesman for the association, called the program “one of the most complicated and counterintuitive systems for ensuring aircraft security.”

Approximately 30 percent of flights to Israel fly through disputed airspace that can increase the workload in the cockpit, making it more likely that pilots may err in entering the security code, according to the International Federation of Air Line Pilots’ Associations. And because it there is no set procedure for how to handle these kinds of pilot errors, critics say, flights can be put in jeopardy.

“People do shoot down airliners, sometimes on purpose,” said Gideon Ewers, a spokesman for pilots association. “Sometimes they shoot them down by mistake. Whether intentional or unintentional, things can happen.”

In addition to safety concerns, international airlines and the European Union say, the program creates logistical problems by separating pilots into those with PINs who can fly into Israel and those who cannot. The director general for the European Commission’s Air Transport Directorate, Daniel Calleja, told the Israelis this could restrict “the ability of airlines to efficiently allocate their personnel.” In a letter sent earlier this month, Mr. Calleja made a veiled threat that this could “have immediate implications on the current air services agreement between the EU and Israel.”

Mr. Ewers said another meeting was scheduled with the Ministry of Transport for later in the week where pilots would ask that the program be scrapped.

The ministry declined to answer questions about the program. But it said in an e-mail message that the security program was still in the trial phase and that a decision on whether to continue it would be made soon.

Ziad Haddad, an international airline compliance specialist, discounted the possibility that commercial airliners were threatened by the program. “I am sure that the risk factor was reduced to the minimum and the Israeli authorities have studied that thoroughly to protect against overreacting or mistakes, meaning that to enter a wrong code or data by mistake will never lead to shooting down the aircraft,” he said.

Richard Bloom, a professor and airline security expert at Embry-Riddle Aeronautical University in Prescott, Ariz., said it was possible that Israel would push back even in the face of strong opposition. “If they have validated some sort of risk that suggests, with all its superficial flaws, it is the right system, I doubt they would share it with many people,” he said.