Considering Pilots, Flight Attendants and Customer Service in Airlines are considered at least tier 2 and possibly tier 1 this statement generally applies.
An employer’s direction to employees performing Tier 1 or Tier 2 work is more likely to be reasonable, given the increased risk of employees being infected with coronavirus, or giving coronavirus to a person who is particularly vulnerable to the health impacts of coronavirus.
Tier 2 would be the minimum as airline employees in customer facing or involved in flight operations can not avoid being in contact with aged or vulnerable unless the airline undertakes not to carry such passengers. It would be easier to require everyone be vaccinated than to discriminate based on age and disability. Aircraft also have limited ingress and egress points and very limited chance for segregation and social distancing, making ruling in favor of mandate almost a certainty.