Beware of overselling the potential of universal fault interrupter (UFI) technology, the Federal Aviation Administration (FAA) advises. In a critique offered in response to coverage of the UFI 3000 device touted by San Diego, Calif.-based TDG Aerospace, the FAA advises that the technology’s limitations need to be weighed against its benefits (see ASW, March 22). As an example, the FAA asserts that arc fault circuit breaker (AFCB) devices will protect the entire length of a circuit, whereas the UFI will protect only what is “downstream” of the device. On the other hand, the FAA said AFCB and UFI devices, whether used separately or in combination, can enhance electrical system safety.

Below, the main points of contention offered by the FAA, with responses from TDG Aerospace:

FAA: If the AFCB is mounted in the distribution panel - and the vast majority of circuit breakers are [installed in this manner] - the entire feed to the load is protected. The UFI will only protect what is downstream of the device.

TDG Aerospace: Both AFCB and UFI are sensitive to series faults (opens) both upstream and downstream. Both AFCB and UFI are sensitive to parallel faults (line-to-line arcs and ground faults) downstream of their position. The decision on where a fault detection device should be located is highly application-dependent. For the fuel boost pump systems, it is understood that the critical portion of the circuit is the (Cont’d on p. pump itself and the local pump wiring. There is little room for de-rating protective devices for this critical application, which demands the highest levels of sensitivity and accuracy.

FAA: The UFI is applicable to three-phase circuits only. The vast majority of loads on a transport aircraft are single phase or DC powered.

TDG: While the UFI 3000 is designed specifically for the protection of the B737-300 center-tank fuel boost pumps, the UFI technology has no such limitation. It can be designed to protect two- and three-phase balanced loads, two- and three-phase unbalanced loads, three-phase loads with or without a neutral return line, single phase loads, or even DC circuits. The UFI can be tailored to operate anywhere there is current flowing in a circuit.

FAA: A UFI or AFCB device tailored for a particular load either will not function or will be prone to nuisance trips on other loads.

TDG: The UFI 3000 is application specific and is tailored to a specific load because the design application (fuel boost pumps) requires it. TDG’s proprietary technology is designed to prevent nuisance faults for each specific application. Additionally, the UFI technology allows for the detection and recording of all electrical faults - although only potentially dangerous events result in a latched condition that removes system power.

FAA: The broad applicability of AFCBs makes part inventory and selection no more problematic than conventional circuit breakers. This is not necessarily the case with UFIs.

TDG: Convenient inventory selection was not considered as a design criterion for the critical boost pump application. Rather, the UFI 3000 was designed in cooperation with both aircraft manufacturers and operators, based on their input of which capabilities would be beneficial in a fault detection device. Consequently, the UFI 3000 is enhanced with additional features such as fault phase identification and non-volatile memory that allows for downloading of relevant operating data that has been identified as beneficial for maintenance personnel.

FAA: Suggesting that UFI offers a single point solution for compliance with SFAR-88 [special federal aviation regulation on fuel system safety] is misleading and dangerous.

TDG: TDG yields to the FAA as to what is the appropriate level of protection for today’s commercial aircraft. TDG Aerospace does not seek to define the “comprehensive” solution to SFAR-88, only to provide the highest level of protection against possible electrical ignition sources.