An airline safety expert says plane crews may be unwittingly compromising flight safety by leaving seatbelt signs on too long.
Greg Marshall suggests passengers may not see the need to remain buckled up if the signs remain illuminated during a smooth ride or if no one has explained to fliers what's going on.
"The seatbelt sign can tend to stay on for long periods of time. There are occasions when I believe the crews simply forget to turn the sign off," said Marshall of Flight Safety Foundation, an aviation safety advocacy group headquartered in Alexandria, Va.
"The intent of putting the seatbelt sign on degrades because passengers get up and walk around the cabin anyway."
Canada's Transportation Safety Board noted in a recent report on 21 turbulence-related injuries on an Air Canada flight from Shanghai to Toronto in December 2015 that passenger compliance with the seatbelt signs may have been affected by the amount of time seatbelt lights had been on.
It said 35 minutes elapsed from the time turbulence preparations started in the cabin to when severe bumpiness began. The cabin lights were low and flight attendants had been moving about, suggesting to passengers that the turbulence was not imminent, the report said.
Canadian aviation regulations require passengers to buckle up during taxis, takeoffs and landings. They must also secure themselves if the seatbelt sign is on or when crew members tell them to do so.
Passengers are also advised, however, to keep their seatbelts fastened whenever they're seated to avoid possible injuries from turbulence.
The industry is aware of the potential for overuse of seatbelt signs.
Transport Canada stated in a 2014 circular that the policies of some airlines to keep passengers in their seats at all times can be counter-productive. It said seat-belt signs should only be lit during critical phases of flight, in cases of turbulence or when the pilot deems it necessary for safety reasons.
"By doing so, passengers and crew members are more likely to understand and realize the importance of the safety belt sign and comply with the instructions when it is illuminated," the circular stated.
The International Air Transport Association advises that seatbelt signs should be used only when necessary "to avoid undermining the importance of the illuminated signs during turbulence or emergency situation."
The TSB report on the Air Canada flight noted that Transport Canada recommends seatbelt announcements be customized with the anticipated severity and duration of turbulence.
"Passengers are more likely to pay attention to and comply with cabin safety information if they perceive it as relevant."
Marshall said policies on seatbelt signs tend to vary greatly from airline to airline. Some carriers leave signs on and don't care much if passengers get up. Others are strict and clashes can occur between flight attendants and fliers used to more relaxed rules.
WestJet spokeswoman Lauren Stewart said in an email that the airline follows Transport Canada's advice and uses the sign only when necessary for safety.
Air Canada noted it, too, follows Transport Canada on seatbelt use and makes announcements about the signs in English, French and other languages, depending on the route.
Spokeswoman Angela Mah said passengers are advised to keep their seatbelts on at all times as a precautionary measure.
Marshall said the decision on when to switch on the signs is ultimately up to the captain, who may be communicating with other pilots about turbulence in the same airspace.
He said he asks an attendant what's happening when he's on a smooth flight and notices the seatbelt sign has been on for a long time.
"The flight attendants ... have actually gone and asked the crew, and the seatbelt sign has invariably been turned off shortly thereafter."
