Here's what happens when airlines receive bomb threats

LONDON (AP) — Hundreds of airline passengers in Europe had their flights diverted or given military escorts this week after a series of bomb threats that officials have said were malicious hoaxes.

It was not immediately known who was behind the threats, which came at a time of rising tensions with Russia and warnings that it may be ramping up so-called hybrid attacks in Europe.

Here's what happens when airlines receive bomb threats.

Assessors determine whether a threat is credible, partially credible or not credible, according to Joji Waites, director of flight safety, policy and regulation for the British Airline Pilots’ Association.

If deemed credible, the flight crew is informed right away and the captain makes all the decisions, guided by a safety checklist, said Waites. If the aircraft is on the ground, that would mean evacuation. If already in flight, the priority would be to land as soon and as safely as possible.

“Pilots are highly trained and skilled professionals. Their expertise is invaluable in ensuring passenger safety and keeping aviation one of the safest forms of transport there is,” Waites said.

Airlines, airport operators and law enforcement generally follow guidelines developed by the European Union Aviation Safety Agency and the International Civil Aviation Organization, which conducts audits to ensure compliance.

Flight crew training includes live situational exercises covering various threats, including how to search for explosives that may have been smuggled on board.

When threats are called in, airline employees are instructed to keep the caller on the line and to gather as much information as possible, according to aviation security expert Philip Baum.

Many of the threats received this week were sent by email, with enough information for authorities to determine that aircraft needed inspection. That can be costly for airlines.

Baum, a visiting professor of aviation security at Coventry University in England, said diverting a flight because of an unruly passenger or a bomb threat can cost up to $250,000.

The costs may be lower in this case because most of the disrupted flights were short-haul, where there is less likelihood of overnight delays, he said.

The intent with these threats “appears to be to sow chaos, uncertainty, about the reliability of air traffic across Europe,” said Jacob Funk Kirkegaard, senior fellow at the Bruegel think tank in Brussels.

The threats could also be testing the relative response time and level of coordination among authorities in different countries, with the aim of identifying weaknesses for future attacks.

“Do the authorities in Poland respond at the same speed and with the same urgency, et cetera, as the authorities of Italy, for instance?” Kirkegaard said, comparing such threats to a “stress test” of the system.

Carlson reported from Brussels and Hadjicostis from Nicosia, Cyprus.