reimbursement for the cost of transport between home and the base airport
This is a type of transport payment. You will need to determine if it is deductible or not. Generally overnight travel and travel between locations is deductible but part day travel is not.
Do not withhold if the allowance is deductible e.g. overnight travel. Withhold for travel payments like part day travel.
Deductible transport payments are not included for ordinary times earnings. Non deductible travel is included for ordinary times earnings
The exempt portion (up to $280.75 per day) is not included for payroll tax purposes and is exempt. The amount above that is included for payroll tax purposes
For deductible travel, show it separately as an allowance. For non deductible travel, include as part of gross payment
If it is overnight transport - Transport. Otherwise, use Gross PAYEVNTEMP47