Editing Avionics software (section)

===Maintenance manual===
As soon as the engineering specification is complete, writing the maintenance manual can start.  A maintenance manual is essential to repairs, and of course, if the system can't be fixed, it will not be safe.

There are several levels to most standards.  A low-safety product such as an in-flight entertainment unit (a flying TV) may escape with a schematic and procedures for installation and adjustment.  A navigation system, autopilot or engine may have thousands of pages of procedures, inspections and rigging instructions.  Documents are now (2003) routinely delivered on CD-ROM, in standard formats that include text and pictures.

One of the odder documentation requirements is that most commercial contracts require an assurance that system documentation will be available indefinitely.  The normal commercial method of providing this assurance is to form and fund a small foundation or trust.  The trust then maintains a mailbox and deposits copies (usually in [[ultrafiche]]) in a secure location, such as rented space in a university's library (managed as a special collection), or (more rarely now) buried in a cave or a desert location.<ref>Personal Information, Robert Yablonsky, Engineering manager, B.E. Aerospace, Irvine, CA, 1993</ref>