Cathay lawyers argued that duty-free sales commissions, line-duty and ground-duty allowances - which attendants earn in the air and waiting for flights - are variables and should be excluded from the calculation.

The dispute stems from claims lodged in the Labour Tribunal about four years ago by flight attendants Becky Kwan Siu-wa, Vera Wu Yee-mei and Jenny Ho Kit-man.

The tribunal initially ruled in their favour and ordered Cathay to pay the shortfall, but the airline won on appeal. That ruling, however, was overturned by the Court of Appeal last year.

The top court reserved its judgment yesterday. It heard that an average daily wage is used to calculate the holiday pay.

Mark Strachan, a Cathay lawyer, referred to the definition of wages under the Employment Ordinance to argue that allowances and commissions should not be included in the calculation. That's because they are money that "may be earned" but not "would have been earned", according to him.

But Chief Justice Geoffrey Ma Tao-li said flight attendants would certainly earn one or other allowance whenever they worked.

Strachan suggested that construction workers were in a similar situation because they did not earn a regular basic salary.

But judges said construction workers differed from airline attendants because they were casual workers.

Strachan, citing previous cases, said a straightforward method should be used to calculate the pay to avoid chaos.

He said including the duty allowance in the pay formula would create a conundrum.

But Mr Justice Kemal Bokhary said he did not think it was unworkable.

The court heard that flight attendants earned commission of 3.5 per cent on duty-free sales.

The court said there was no need for Martin Lee Chu-ming SC, who represents the attendants, to reply.