A European mandate calling for mode-S transponder upgrades in transport-category airplanes is causing confusion for some U.S. business jet operators as they struggle to interpret the rule’s fine print and decide whether it applies to them.

The March 31 deadline requires changes to mode-S transponders to meet specifications for two upgraded levels of functionality, elementary (ELS) and enhanced (EHS) surveillance. Both levels will be required over certain parts of Europe at the end of the month, but some operators can apply for exemptions to the EHS portion of the mandate, giving them until March 31, 2009, to comply. The confusion apparently stems from misunderstandings about which airplanes are eligible for exemptions and which are not. 

“Operators can request, on a case-by-case basis, that their airplanes be exempted from the enhanced-surveillance requirement,” said Arnold Oldach, marketing manager for surveillance and datalink products for Rockwell Collins. But, he stressed, securing an exemption from Eurocontrol is possible only if an operator cannot comply with the mandate because of a technical or equipment shortcoming. “If your airplane is EHS capable, you will not get an exemption,” he said.

Scores of airplanes with older analog air-data systems cannot meet the required parameters for enhanced surveillance and are therefore eligible for exemptions. Most modern transatlantic-capable business jets, however, can meet the specifications for EHS without difficulty. For those operators, there is little hope of avoiding the mandate, Oldach said.

The fact that the EHS requirement applies only to the airspace over the UK, France and Germany is of little consolation because flight crews cannot be certain they’ll be able to avoid overflying these countries. Business jet operators who try to fly to Europe after March 31 and have not upgraded to EHS standards or secured exemptions face unpleasant consequences. “I’m not exactly sure what they’ll do with an operator who’s not EHS capable and hasn’t received an exemption,” Oldach said. “They might stick you at an altitude you don’t like, or they might tell you to turn around and go home.”

Faced with such uncertainty, the majority of operators whose aircraft are EHS capable and who plan to make trips to Europe in the near future are bringing their airplanes into modification shops for upgrades. ELS and EHS provide flight identification data to mode-S radar sites. Enhanced surveillance sends additional information known collectively as downlink aircraft parameters (DAP). The full DAP list includes: magnetic heading; indicated airspeed and/or Mach number; vertical rate (climb/descend); selected altitude; groundspeed; roll angle; track angle rate (or true airspeed if track angle rate is not available); and true track angle. Wiring changes are needed to ensure this information is being sent to Eurocontrol radars.

Operator ‘Panic’
Europe needs mode-S because the so-called Core Area of Europe (that part of the continent that is subject to extremely high air traffic density) is covered by secondary surveillance radar systems that have reached their life limits. Radio frequency pollution, lost targets, identity errors and mode-A code shortages have become commonplace in the core as a result. Mode-S enhances the capability of secondary radar by establishing selective and addressed interrogations with aircraft within its coverage area. Such selective interrogation improves the quality and integrity of the detection, identification and altitude reporting.

An FAA official said some business jet operators he has heard from “are in an absolute panic” about the EHS requirement because they have done little or nothing to prepare for the mandate. On average, the upgrade involves three to four days of downtime to make wiring changes between the air-data computers and FMS.

Operators who can obtain an exemption should file the paperwork now if they plan to make a trip to Europe anytime soon. Approvals, according to Eurocontrol officials, can take a month or longer to process.

John Law, mode-S and ACAS program manager for Eurocontrol, said more than 90 percent of affected airliners have undergone upgrades and the remainder, for the most part, have obtained waivers. “Unfortunately, we cannot easily split out the figures for business jets,” he said. Noting that figures for N-registered airplanes are available, he said 519 airplanes with N-numbers have been deemed EHS compliant so far, while about 400 have been granted long-term exemptions because they cannot meet certain EHS parameters.

For more information, visit Eurocontrol’s mode-S Web site.