Avionics

Euros Seek Transponder Enhancement

Some European countries are mandating modification of ATC transponders whereby elementary surveillance (ELS) and enhanced surveillance (EHS) functionality is added. This requirement originated with Eurocontrol. These things happen. Unfortunately, many airlines have not treated the mandate (March 31, 2005) seriously. The requirement was established per a European document called an aeronautical information circular (AIC) issued in December 2000. It was designated as an information circular and was not taken as seriously as an airworthiness directive. Therefore a lot of airlines tried to negotiate the new mandate with authorities but without much success. Some airlines created a problem for themselves by waiting too long to begin the modifications.

Complicating the situation is that it is not clear what must be done to comply. It seems that wiring modifications are required to connect transponders to the FMC, GPS, or IRU to obtain a set of parameters that will be transmitted to ATC. To do this, the transponders should be modified as well. Some transponders (some Rockwell Collins models) cannot be modified and must be replaced. ACSS transponders can be modified, which could be more cost effective.

The biggest problem is that manufacturers are not able to comply with the mandate by timely delivery of service bulletins, mod kit, and LRUs. The airlines could be at fault, too, for unfreezing at such a late date and realizing that the mandate is so near. Airlines are concerned now because even if they want to comply they can't due to the fact that the bulletins and LRUs for aircraft modification are not yet available. The most optimistic prediction is that the modifications could begin in late 2004. If Boeing certifies new transponders in August, the activation service bulletins will be available in September/October and then there will be just six months to modify the whole fleet. The lucky few with a fleet of one can do it easily, but if the airline has 100 aircraft that will be different.

According to a Boeing prediction, approximately 120 hours and four days ground time is required to accomplish the modifications. That means a lot of non-revenue days for the fleet. If an airline decides to go for the supplemental type certificate solution, then certification can be planned before August 2004. The LRU manufacturers should make the new transponders available by early third quarter 2004. Would they be able to deliver so many transponders in the next couple of months? Based on experience with RVSM, 8.33 channel spacing, and FM immunity, it is evident that the LRU vendors are underestimating their share of the market and are not able to provide enough LRUs by the end of the modification period. Based on the same experience it can also be concluded that airlines are making the same mistake all over again by hoping that the mandate is a soft mandate and that the deadline will not stay solid. Nevertheless, if the EHS/ELS wiring modifications had been started in 2000 (immediately after the aeronautical information circular was issued), airlines could have saved a lot of ground time to modify their fleet. All wiring could be installed during C- or D-checks and the transponder replacement could be done during an A-check, (not one additional hour of ground time on the top of the standard check.) That approach would be more cost effective than waiting and praying that the mandate will be postponed. The wiring job could be done in any case.

Fortunately it seems that airlines are good at doing modifications at the last possible moment. It will cost a lot of unexpected ground time, but in the end it will be done before the deadline of March 31, 2005.

Work Indoors with a GPS Repeater

A lot of airlines are busy installing TAWS (terrain avoidance and warning systems) in their aircraft. The TAWS modification is also a perfect opportunity to upgrade the navigation system and introduce GPS as a position sensor. It is an expensive job and costs a lot of effort to do the installation during a regular C- or D-check. However, some aircraft are not scheduled for C- or D-checks before the JAA/FAA-mandated deadline. Those aircraft must be modified during dedicated ground time. Depending on the aircraft type and the magnitude of the modification, the planning department will calculate the ground time. For a 747-400 it will usually be five days. The last two days the technicians are busy testing all affected systems, which applies to any area where wiring is added or worked on.

Here comes the glitch. The GPS cannot be tested inside the hangar. Even if the doors are open, there is no GPS signal. On the last day the modification team will need to call the tug and roll out the aircraft onto the ramp. After several minutes there will be a suitable GPS signal. The last couple of GPS-related tests can be accomplished, and the aircraft is ready for operation. Now and then, there is a problem and the GPS doesn't work. After some troubleshooting, the problem is usually isolated to the wiring at the avionics rack. The aircraft must return to the hangar for the fix. But the aircraft was just parked outside and the tug driver is on another job on the other side of the airport. The whole shift of technicians is now waiting for an hour to get back into the hangar to fix the wiring problem and then pull the aircraft back outside again to try that GPS test again. A lot of man-hours are lost.

Here is a tip, which will save a lot of time and trouble. There is a GPS repeater on the market. One type is made by GPS Source (www.gpssource.com). Install that device in your hangar and you will solve a lot of problems. It is as simple as that. There is an antenna (which can be installed on the roof of the hangar), a long coax cable, a small power supply, amplifiers, splitters, and transmitting antennas. The transmitting antenna can easily be installed inside the hangar at a dock. According to the specifications, the range of the transmitting antenna is 30 meters (about 100 feet). If your hangar is big you would need more then one antenna, for a small hangar just one. The vendor will even issue a certificate declaring the exact position transmitted inside your hangar.

The aircraft modification team can now accomplish all testing in the hangar. When you call your tug driver to pull the aircraft from the hangar, you can be sure that aircraft is really ready. No sweat, no uncertainty about whether the GPS in the aircraft will work or not, or if there will be enough time to fix a possible problem.

The repeaters are not expensive. For a couple of hundred dollars, you can have all the hardware. The most expensive factor is the man-hours needed for installation of the antenna on the roof of the hangar. But it is worth it. Prevent just one return to the hangar for wiring repairs and your investment is earned back. And once the system is installed, the technicians can use it for testing of GPS systems during any regular check.