In a letter to Canada's air security agency, the federal privacy commissioner's office also raises a flag about possible misuse of passenger information gathered through the proposed program.
"We believe that the information collected is adequate to identify an individual and may be easily linked to other sources of identifiable information," says the letter from Steve Morgan, director general of the privacy commissioner's audit and review branch.
The Canadian Press obtained a copy of the March 2011 letter spelling out the privacy czar's concerns about the passenger behaviour observation program.
The Canadian Air Transport Security Authority, responsible for air passenger screening, has been studying the possibility of such a program to thwart terrorist plots. It notes the commission of inquiry into the 1985 Air India bombing warned against relying exclusively on technology for vetting air passengers.
In a pilot project at the Vancouver airport from February to July of last year, special officers were on the lookout for suspicious behaviour, such as passengers sweating profusely, or wearing a heavy coat on a hot day.
The uniformed officers proceeded to question passengers who were behaving in an unusual manner.
The letter says the commissioner's office has asked for "empirical evidence" that demonstrates the technique's effectiveness in spotting would-be terrorists. It is especially interested in evidence comparing it with the tactic of random questioning, as well as reports on how well passenger observation works in other countries.
The letter also raises concerns about possible profiling based on race, ethnicity, age or gender.
In a May reply to the privacy commissioner's office, the air transport security authority says consideration of privacy issues has "been at the core" of the pilot program and that privacy risks have been "appropriately mitigated."
On the question of profiling, the air security authority says it has incorporated feedback from the Canadian Human Rights Commission and the Cross-Cultural Roundtable on National Security, composed of citizens of various backgrounds.
The agency also says it has created a standalone database for the program, and does not disclose or share the personal information it contains. "Access to this database is restricted to those who require it to carry out their responsibilities and CATSA is of the opinion that there is sufficient oversight in place to prevent cross-referencing with any other existing database."
The air security authority has also assured the privacy commissioner the passenger behaviour officers will not collect personal information that could identify an individual, said Anne-Marie Hayden, a spokeswoman for the commissioner's office.
"That said, we have not yet had the opportunity to view samples of information collected to evaluate."
Concerns remain about profiling, effectiveness and the overall need for the program, Hayden, added.
The air security authority's preliminary report on the Vancouver pilot project, also released under Access to Information, says the exercise "met each of its objectives."
The agency withheld statistics on the number of passengers referred to the RCMP or airport security after displaying "irregular behaviour" during pre-board screening. However, the report does say one arrest resulted.
Passenger behaviour observation could be integrated into pre-board screening "without affecting the amount of time it takes a passenger to move through the checkpoint," adds the report.
The Transport Department, which will decide whether to roll out the technique nationally, says it is "too early to tell if there would be value in establishing a national passenger behaviour observation program."
"Transport Canada is conducting further analysis, assessment and consultations with industry and other federal partners," the department said in a statement.