Avionics Etc.

Old Birds Want to Fly

By Marijan Jozic

There are a lot of old aircraft parked in dry environments. Some are parked for two or three years or more. Some will stay forever but others need to be activated, right now. Reactivating a stored aircraft is quite a job, and there are unexpected surprises as well.

The problem is not in performing the work but in getting engineering done and all the parts delivered on time. At the present, engineers are not interested in messing with old 747s. There is no engineering skill in the field to do avionics mods on the old birds. The young engineers don't like to mess with discretes, synchros, servos, pot meters, and other fascinating components. It is much easier to work with high-speed networks and modern databusses.

But old birds want to fly and they need special care. The owners want the best work possible for the lowest cost. The owner also wants to navigate using global positioning system (GPS). They want the thrust reverser actuation system lock airworthiness directive (AD) complied with, but they don't want to pay $500,000 for the kit. They want enhanced ground proximity warning system (EGPWS) but they don't want to spend much for it. They are trying to avoid emergency locator transmitter (ELT) installation although they are going to fly more than two hours above the ocean.

It appears that some airlines made bad decisions in the past, during the terrain collision avoidance system (TCAS) mandate. At that time they were replacing the ATC mode C transponders with mode S. To save some money they decided to replace just one mode C transponder with Mode S. They are now flying with one mode C and one mode S Transponder. With the European Elementary/Enhanced Surveillance mandates, they will have to spend more money to design the replacement of the mode C transponders with mode S. One problem is that young engineers are not experienced in designing the change. Some of the young engineers have never heard about mode C but they can tell you anything about the electronic flight bag. They were playing in the sand when we (old guys) were installing TCAS and mode S on 747 Classics. Furthermore, the FAA will not accept the way we used to modify aircraft in the 1980s. There are new requirements such as high intensity radiated fields (HIRF), lightning, and wire-separation. These were not known and required when the aircraft was designed. Now we have the unique situation where the whole old aircraft doesn't comply with those requirements but all new systems must comply.

It's a lot of work to fix the old birds, but it is also a lot of fun. The important question is when to stop investing in the old aircraft. Keeping the aircraft in the fleet requires effort and cash. There is another absurd situation with older aircraft. For example, a new owner purchases aircraft from different sources. Some of those aircraft were modified to a certain level, some were not. The problem is to establish which will be the company standard. This is not so easy because it can cost a lot of money in the long run. All other aircraft have to be modified to copy the fleet standard. The engineers may even have to remove more sophisticated systems from one aircraft to match the fleet.

Maybe the biggest problem of all is documentation. Many early owners decided not to spend money on updating manuals. All the new modifications are part of the temporary revision, but temporary can't be stretched forever. When you accept the job to do the mod, you are on thin ice: you cannot blindly trust the manuals, the old line replaceable units (LRUs) are not obtainable in the secondhand market, and engineers are not experienced in designing mods on old aircraft. The maintenance company could subcontract a modification to an integrator or mod-house but sometimes they can't help or the work isn't remunerative.

If you must be take on a modification on an old aircraft, it is easy for the budget to explode. Nobody will express sympathy when they fire you for underestimating the job and for making the project a disaster.

Designing cabin modifications is not so difficult. Cabin systems are almost standalone. But modifying the cockpit is hard; it requires a lot of interfacing with old systems. And that is where the engineering fun starts. The fun ends the moment the old bird really gets old and when it gets parked in the desert again, which means that all those modifications are not required to last more than five or six years. Even then, the engineer will be asked to remove the new equipment from the old aircraft and try to use it in other aircraft in the fleet. The good old stuff is too expensive to leave in the desert. Only the aluminum junk, which used to be an aircraft, will lie somewhere in the desert between coyotes and cactuses, reminding us about the big engineering adventures in the early years of the third millennium.