Leading Other Aircraft Astray With Improper ADS-B & Transponder Tests
Since the roll out of ADS-B out systems, the Houston Flight Standards District Office has received a number of reports that the aircraft being tested has transmitted position information, including a simulated altitude. This appears to be happening when conducting ground test of transponders and ADS-B Out systems.
What makes this situation a problem is that aircraft in flight received this test information, and when the test aircraft’s simulated ADS-B altitude was too close to that of another aircraft in flight, let’s just say that the pilots of the flying aircraft were more than a little bit concerned.
In one instance, said FAA Safety Alert for Operators (SAFO) 17002, which addressed this problem, the ADS-B Out test that transmitted a simulated altitude triggered a TCAS (traffic alert and collision avoidance system) resolution advisory (which way to go, such as climb, to avoid a midair collision) on a Boeing 737 on an approach.
Given Bush Intercontinental (IAH) and Houston Hobby Airports (HOU) proximity to TCAS-equipped aircraft conducting terminal operations, it behooves everyone to invest a few minutes in reading the SAFO and ensuring that all test operations follow the proper procedures. And this applies to the operators of all aircraft equipped with ADS-B.
Following the proper procedures is the easiest way to avoid leading airborne aircraft astray with ghostly ADS-B position and altitude reports from aircraft being tested on the ground. The antennas must be shielded to prevent position and simulated altitude reports being transmitted to the air traffic control system and TCAS-equipped aircraft in the area.
To test the altitude reporting component of these systems, the test equipment is connected to the pitot-static system, which allows the technician to raise or lower the air pressure the system senses. This simulates the air pressure at different altitudes.
As a backup to following the proper transponder and ADS-B test procedures and effective antenna shielding, when required, technicians testing these systems should also notify the nearest air traffic control facility (that would be the Bush Intercontinental or Houston Hobby tower) about the impending tests.
Before they call, they should review the relevant guidance in the current Advisory Circular 29-151, “ Airworthiness Approval of TCAS II and Associated Mode S Transponders,” AC 43-6, “Altitude Reporting Equipment and Transponder System Maintenance and Inspection Practices,” and AC 20-165, “Airworthiness Approval of Automatic Dependent Surveillance – Broadcast Out Systems.
Bush Intercontinental Control Tower (281) 209-6600
Hobby Airport Control Tower (713) 847T1406
Glen Longnion, Houston FSDO FAAST Team Program Manager
glen.longnion@faa.gov (281) 929-7009
