on decommissioned aircraft
Comprehensive programme for technical care
Following the attacks on 11 September 2001 and the outbreak of the SARS epidemic, Lufthansa and many other airlines decided to decommission a part of their fleets, at least temporarily. But an aircraft which normally flies thousands of kilometres every day cannot simply stay on the ground for weeks or months without special measures being taken for its care and protection. Besides good planning, the appropriate technical support is needed here so that the airline can stay flexible in its ability to react to changes in conditions. The manufacturers give precise guidelines for handling parked aircraft in an aircraft maintenance manual (AMM).
Airbus and Boeing differentiate between various parking scenarios. Airbus starts with a programme for aircraft which will remain on the ground for a maximum of two days. A further scenario has been drawn up for the decommissioning of an aircraft for a period of up to twelve weeks – in this case, the aircraft is maintained in "flight ready condition,– meaning that it can be returned to the operative fleet within a comparatively short time. Finally, the scenario "Storage– describes the measures to be taken when an aircraft is decommissioned for up to two years. Boeing has drawn up two similar programmes: the distinction in this case is between the parking of an aircraft for up to seven days and the "Prolonged Parking,– which is comparable to the "Storage– scenario at Airbus.
The AMM contains detailed descriptions from the manufacturers for the scenarios described above as to the maintenance measures which must be taken for the decommissioning itself and before the aircraft is returned to operation. Furthermore, there are various inspection procedures, depending on the length of time of the decommissioning, which must be performed at regular intervals. If an aircraft decommissioned for up to seven days (Boeing) or twelve weeks (Airbus) is handled by Lufthansa Technik, the instructions in the AMM are followed precisely. However, Lufthansa Technik has developed and issued as an Engineering Order (EO) a tested and approved procedure based on the AMM for aircraft which are to be out of service for a longer period – the company's many years of experience made it possible to optimize some of the instructions in the AMM. Procedures not applicable at Lufthansa were cut out, the instructions were supplemented by other sensible additional inspections and adjusted to take into consideration the latest developments.
"Aircraft in flight ready condition"
The scenario "Aircraft in flight ready condition–, the decommissioning for up to twelve weeks, comprises three different work packages. First there is a procedure for parking, then an idle time inspection is required at 15-day intervals, and finally there is a work package "Return to operation.– If regular maintenance work on the aircraft is planned during the decommissioned phase (e.g., work which is performed according to specific calendar dates), it is carried out additionally. Before the aircraft begins flying operations again, a routine service check (S-Check) is performed. When proper advance notice has been given, an Airbus parked in "flight ready condition– can be prepared for resumption of operations within two to three days.
The measures for "Storage– or "Prolonged Parking– are far more comprehensive than for a short-term decommissioning. An average of 300 working hours must be allowed for the deactivation of an aircraft alone. The periodic inspections are performed at different intervals; some of the inspections are more, some less complex. To start with, the "Storage Procedure– includes essentially the measures which are also required for short-term parking. But beyond this, extensive preservation work is done: the flight controls are greased, and all of the unprotected aluminium and steel parts on the aircraft exterior are treated with corrosion prevention agents.
Furthermore, the engines and the APUs are coated with a preservative before the protective cover is placed over them. The tanks are filled to a level of 90 percent, also an anti-corrosion measure – in addition, a special protective fluid is mixed with the aviation fuel. The fluid level of the hydraulic system is lowered, and the landing gear is packed in grease. Rubber parts of the landing gear are treated with talcum powder so that they remain supple. To protect the cabin, the sunshades on all of the windows are closed and the windows themselves are covered with a protective layer. At a large station with a lot of preparation time, it takes about a week to conduct all of the measures necessary to ready the aircraft for a return to service.