Airbus and Boeing are again engaged in a serious dispute over comparative performance figures for the Airbus A380 and the Boeing 747-8.

Following a decision by the U.K. Advertising Standards Authority (ASA) to dismiss an Airbus claim over what the manufacturer considers to be misleading advertising content, John Leahy, Airbus Chief Operating Officer Customers, says Boeing’s assumptions behind its performance claims are “as outdated and obsolete as the 747.”

Airbus had initially reacted to the Boeing advertisement in question last year by placing counter-advertising in the trade press showing a 737 “Pinocchio” aircraft, alleging that its competitor was not telling the truth about comparing the 747’s and A380’s performance. Boeing had initially claimed a 26% trip cost advantage for the 747-8 over the A380, as well as 8% better unit costs.

The ASA states in its report that the intended audience of the ad is “involved in the decision-making process to purchase large aircraft, and would have a high-level understanding in this area and would be familiar with the method of comparison used by Boeing.”

The U.K. regulator also concluded that the audience was “unlikely to make a purchase decision without seeking a great deal more information on the potential advantages of the airplane, based on their own specific requirements.”

In a statement, Boeing says it thanks the ASA for the “decision to dismiss the unfounded complaints. We are pleased that our advertisements underlining the advantages of buying Boeing products have been supported.”

Airbus, in contrast, claims that the decision has “not taken equivalent comfort standards into account. While the A380 features a total of 525 wider seats in all classes, more legroom, more comfort and space, Boeing squeezes 467 seats into the 747-8’s dated fuselage, confirming Boeing’s legacy comfort standards dating back to the 1980s.”

Airbus also insists that under comparable conditions, the A380 has a “significantly lower fuel-burn per seat compared to the 747-8.”

Leahy says that Boeing “continues trying to mislead the public by claiming a ‘standard layout’ that actually has never been sold or installed on any of their aircraft. Boeing should stop trying to mislead and acknowledge that the old 747 ‘reference’ layouts have been overtaken by reality.”

Given that the 747-8 is currently only operated by one passenger airline (Lufthansa), it is difficult to find independent operations data to verify the performance and cost claims made by Boeing and Airbus. However, one airline industry source with detailed inside knowledge of performance data for both aircraft on comparable routes and layout standards says there is hardly any unit cost difference between the 747-8 and the A380. Even so, that data does suggest a trip cost advantage for Boeing in excess of 20%, the official says. Unlike the unit cost figures, which appear to be off for both the Boeing and Airbus claims, the trip cost level would be relatively close to what Boeing markets for its largest aircraft.

Boeing only has orders for 40 747-8 passenger aircraft, 16 of which have been delivered. Eight are flying with Lufthansa and eight are VIP aircraft. Korean Air and Air China have ordered five each, while Arik Air has bought two.

Airbus has 262 orders for the A380, 106 of which have already been delivered.