What’s up with WAAS? That’s the question countless business jet pilots have been asking since the FAA announced plans to publish thousands of WAAS LPV (lateral precision with vertical guidance) approaches at U.S. airports while simultaneously making it difficult–or in some cases impossible–for operators to gain approval to fly the procedures.
Officials from the FAA and Universal Avionics plan to meet this month in Washington to discuss a topic that has been a source of endless frustration for scores of these business jet operators: the inability for them to obtain approval to fly WAAS LPV approaches without first subjecting themselves to a months-long STC process that requires the submittal of issue papers for a particular aircraft model.
There are now more LPV approaches in the U.S. than ILS procedures, yet only a small handful of Part 25 business jets can take advantage of the GPS-based landing capability because of the complicated STC rules. This despite the fact that any Cessna 172 equipped with a panel-mount GPS WAAS navigator with LPV approaches loaded can fly the more than 1,330 procedures in place at more than 830 airports around the country.
Next month’s meeting between officials from Universal Avionics and representatives from various FAA branches will seek to clarify and perhaps amend the rules that prevent field inspectors from signing off on the LPV portion of an FMS equipment upgrade in Part 25 airplanes. Universal was the first to obtain TSO C146b approval for a WAAS flight management system, but since then has had little luck freeing a certification logjam that is preventing buyers of its FMS equipment from gaining LPV approval.
“The problem we’re running into, and the subject of our meeting with the FAA, is that several thousand aircraft that are candidates for WAAS upgrades today enjoy fully coupled, 3-D approach capability, yet for an applicant to upgrade to WAAS there is policy from FAA flight standards that disallows field approval of a WAAS upgrade that contains the LPV approach capability,” said Bob Uhde, director of certification and program management for Universal Avionics in Tucson, Ariz.
Some business jet operators have installed WAAS-capable FMS units from Universal, but they are awaiting LPV approval through the often long and cumbersome STC process. As the FAA rules are written, inspectors are prohibited from granting LPV approvals through the Form 337 field approval process. A Gulfstream III operator recently related the tale of his operation’s so far unsuccessful attempt to install a pair of LPV-approved Universal UNS-1Ew FMSs to replace the airplane’s UNS-1C+ with coupled Vnav capability. “The FAA is building LPV approaches and at the same time making it very difficult for operators to use them,” the operator wrote in an e-mail message.
Universal Avionics so far has created only a single issue paper for a Part 25 business jet, the Challenger 601 that it owns. If an operator wants to add only WAAS capability an issue paper is not necessary, but the addition of LPV capability triggers the requirement. Some installation centers are installing WAAS FMS equipment with LPV disabled using the field approval process. The GIII operator reports it is now expecting the LPV STC to be completed in February or March and in the meantime is flying without the capability.
“When operators who want to upgrade to WAAS LPV are turned down by the flight standards branch,” Uhde explained, “they are told to go to the ACO [aircraft certification office] and obtain an STC. The ACOs in general have been telling those folks that it’s going to be a six- to eight-month process and include issue papers, and several have walked away entirely, several were wired up for the retrofit but had to back off and put alternate equipment in, and it has just gotten to the point where it is a big mess,” he said.
Such an installation requires not only an STC but also an issue paper for the particular model receiving the equipment. Installers have had a difficult time satisfying this requirement because the wait time for the approval from the start of the STC process is running so long because of ACO workload.
The FAA has held that inspectors are incapable of evaluating appropriate and proper coupling between the WAAS FMS and the flight guidance system. “We are making the argument that if the installation is already coupled and we are not changing any of that integration, then they should be able to accept that” through the field approval process, Uhde said.
Universal now lists in its FMS installation manual a list of aircraft and compatible flight guidance systems that have been demonstrated to be approved for 3-D lateral/vertical coupling, as well as a decision tree that an FAA inspector could use to validate a number of check points in the process and feel comfortable that he can sign off the airplane. The manual also includes provisions for discrete output for wiring LPV annunciator lights in the cockpit, as well as guidance about how to disable ILS annunciations on certain older EFIS displays.
Other avionics makers are affected by the FAA rules as well, and even the FAA has faced a long road obtaining approval for its airplanes. Rockwell Collins has signed a contract with the FAA to add WAAS LPV functionality to the agency’s fleet of flight inspection Challenger 604s.
So what does Universal Avionics anticipate will happen at its upcoming meeting with the FAA? “We hope to gain recognition of the fact that there are existing integrations in many different aircraft types with many different flight guidance systems that are fully capable of being demonstrated for field approvals,” Uhde said.