As Boeing 787s re-enter service on routes around the world following the aircraft’s prolonged grounding for battery problems, the company is already busy resolving other issues that were emerging before they ceased flying in mid-January.

Most of these problems, such as a string of failures concerning power panels in the electrical system unrelated to the later lithium-ion battery problem, fell into the ‘teething trouble’ category which Boeing uses to describe the steep learning curve of early service life.

These issues impacted the early dispatch reliability of the aircraft, giving it a reliability level in the high 90% levels, roughly similar to the initial performance of the 777-200 shortly after its entry into service in mid-1995.

Although fixing many of these issues pale by comparison with the engineering resources involved with solving the battery problem, at least one concern with the operation of the auxiliary power unit (APU) has prompted Boeing and the unit’s manufacturer Hamilton Sundstrand into a design revision.

Operators have discovered that after the APS5000 APU is shutdown with the inlet door closed after landing, heat continues to build up in the tail compartment. After some 20 min. this causes the rotor shaft to bend or ‘bow’, and the shaft takes up to two hours to straighten back out.

As many 787 operators, including All Nippon Airways (ANA), have flown the aircraft on shorter routes with reduced turnaround times, this has resulted in restrictions on when the APU can be restarted. An advisory bulletin from United Airlines says that if an APU start is attempted 20-120 min. after shutdown with the inlet door closed, the “bowed rotor shaft can cause turbine rub and significant damage.” If such an event occurs, an advisory message on the engine indicating and crew alerting system shows the APU failed to start and requires the unit to be inspected with a borescope.

Boeing acknowledges that “heat conditions have been found to sometimes influence 787 APU starting performance. As a result, operators have been provided a revised operating procedure that has eliminated this finding. An improvement to the APU is being introduced in the next few months to remove the operating procedure.”

The revised operating procedure calls for the APU selector switch to be put in the ‘on’ position on the last shutdown which will open the inlet door, allowing the unit to cool down. The door must remain open for 40 min. before closing it in order to enable the APU to be restarted.

The notice indicates that the APU could be re-started without causing damage if it was re-activated within 20 min. of shutdown, or after 120 min. had elapsed.

The revised procedure also has connections with the operation of one of the 787’s two lithium-ion batteries. The notice contains a precautionary note that advises against using the APU battery power to keep the door open as this will “only have about 15 min. before being discharged.” It adds that ground power must be used to keep the APU door open for 40 min. and warns that, if this is disconnected, the door will close even with the APU switch on the flight deck remaining in the ‘open’ position.

Boeing declines to specify the design changes that will be made to improve the cooling and ventilation of the APU compartment.

In the meantime, Boeing continues to modify the battery system on the last of the original 50 aircraft delivered up to the grounding in January. As of May 21, the company had completed work on 45 of which 40 had flown. It has also delivered the first two new 787s with the revised battery systems installed as new while still at the Everett production site.

United Airlines resumed 787 flights on May 20 with a service between Houston and Chicago. The airline, which currently has six 787s, expected to bring its complete fleet back into service within days and will launch international flights with the aircraft on June 10 with a service from Denver International Airport to Narita International Airport in Tokyo. Other long haul flights from Los Angeles International Airport to Shanghai Pudong International Airport and George Bush Intercontinental Airport in Houston to London Heathrow Airport will be added in the summer months.

ANA will resume services with its 18-strong 787 fleet from June 1, and plans to introduce the type on additional international routes later this summer including Narita to Beijing Capital International Airport and Shanghai and Tokyo Haneda Airport to Taiwan Taoyuan International Airport.

This increase will increase to five the overseas destinations served by ANA’s 787 fleet.

Japan Airlines, which operates seven 787s, also is expected to resume flights on June 1, while Ethiopian Airlines became the first to operate the 787 on a commercial service since the grounding when it flew the aircraft between Addis Ababa Bole International Airport and Jomo Kenyatta International Airport in Nairobi on April 27.

LOT Polish Airlines is scheduled to return its aircraft to service on June 5 with a flight from Warsaw Chopin Airport to Chicago O’Hare International Airport, while Qatar Airways resumed 787 services with a flight from Doha International Airport to Dubai International Airport on May 2.