Boeing, General Electric and Cargolux are in the midst of renegotiating the impact of a 2.7% fuel burn performance shortfall that unexpectedly prompted the cargo airline late Friday to suspend first delivery celebrations for the 747-8 Freighter planned for yesterday.

Although Cargolux had earlier agreed to a form of compensation for the long-delayed aircraft and its acknowledged fuel burn issue, the deal was thrown out at the last minute by a trio of Qatar Airways representatives, who formally assumed a 35% stake in the cargo airline on Sept. 11. At a board meeting just five days later, Cargolux says it voted to reject the deliveries planned this week due to “unresolved contract issues.”

The original deal between Qatar and Cargolux was reached in June, when an agreement was signed in Luxembourg by Qatar Airways CEO Akbar Al Baker and Cargolux President and CEO Frank Reimen. However, the agreement required three months to be ratified by the two governments, and formal clearance came through just a few days before the initial deliveries were due to take place; the first was originally scheduled for Monday and the second tomorrow.

It is thought Al Baker’s group insisted that Cargolux receive additional compensation for the performance shortfall below initial guarantees promised by Boeing and GE. Program sources say the “disagreement is over how much is owed them.”

Neither Boeing nor GE is willing to comment on the renegotiations.

The abrupt turnaround in attitude at Cargolux toward the 747-8F is exemplified by statements made by Reimen as recently as Sept. 2, when he described the aircraft as setting “new standards in efficiency” and featuring “greater fuel economy and the lowest operating cost of any large freighter.” Reimen also described the stretched freighter as “a genuine industry game changer.”

At the heart of the issue is a 2.7% fuel burn shortfall discovered during flight tests on the initial airframe-engine combination. GE is developing a performance improvement package (PIP) for the GEnx-2B engine powering the freighter, but this is yet to be developed and tested and is not scheduled to enter service until the third quarter 2013. Furthermore, GE and Boeing analysis suggests that even then it will account for only 1.6% of the shortfall, leaving an additional 1.1% still to be recovered.

GE is building the first test engine to incorporate the PIP and plans to run it for the first time in January 2012. Boeing and GE also have agreed to continue with additional performance upgrades beyond the initial PIP package. These are aimed particularly at freeing up cargo operators from payload restrictions on longer-range routes. Lufthansa, which will take delivery of the first passenger versions of the 747-8 powered by the same engine, says the route structure on which it plans to use the aircraft means the shortfall will have no effect on its operations.

The GEnx-2B PIP is based on the improvements developed for the upgraded version of the GEnx-1B sister engine, now powering the 787 in the final phases of certification testing. Although the baseline design of the 747-8 engine was originally finalized in May 2006, it adapted configuration changes made as a result of lessons learned from early tests of the -1B engine. Subsequent PIPs developed for the 787 engine formed the basis for the 747-8 engine upgrade when tests of the -2B on GE’s flying testbed revealed a fuel consumption shortfall.