Before understanding the concept of SETWA – Single Engine Taxi Without APU we need to understand something about designated fire zones and JAR/FAR regulations related to same.
Designated fire zones are specific areas within an aircraft. These zones are at a higher risk of experiencing fires, which could be extremely dangerous for the safety of the aircraft, passengers, and crew. As a result, these zones are considered critical areas where fire suppression measures are essential. Special firefighting systems and precautions are put in place to control or extinguish fires in these designated fire zones to ensure the safety of everyone on board.
JAR/FAR 25.1195 compliance requires two discharges with adequate agent concentration in each designated fire zone aimed at ensuring redundancy and effectiveness in extinguishing fires or controlling them in the event of an emergency. Having two discharges provides a backup in case one system or discharge fails to operate correctly, which enhances the overall safety of the aircraft.
When dealing with an engine fire, it is important to first shut off the affected engine before discharging the fire extinguishing bottles. However, in the case of an Engine 1 fire occurring during a situation where Engine 2 is already turned off (SET-IN, ENG 2 OFF), the aircraft relies solely on battery power once Engine 1 is shut down.
Notably, the squibs for Bottle 1 are powered by the Hot Bat Busses, while the squibs for Bottle 2 are powered by DC2. Consequently, in this scenario, only Bottle 1 will be available for use (against JAR/FAR 25.1195 compliance requirement).
This is why, on non-modified (non-SETWA) aircraft, it is mandatory to have the APU running before shutting down Engine 2.
SETWA is a wiring modification in the pylon and around the engine fire handle. It ensures the continuous electrical supply to the squibs of Bottle 2, even when the aircraft is operating on ‘Batteries Only.’ This modification can be installed in a relatively short period, typically during an overnight shift.”
Single Engine Taxi Without APU (SETWA) is an upgrade available for A320ceo Family aircraft. A320ceo family aircrafts by default need APU during single engine taxi. For A320neo family aircrafts, APU is not required for SET IN as the wiring is already modified as per SETWA.
https://www.govinfo.gov/content/pkg/CFR-2010-title14-vol1/pdf/CFR-2010-title14-vol1-sec25-1195.pdf
Related Queries – FAQs:
Q: What is JAR/FAR 25.1195 compliance, and how does it relate to fire suppression in designated fire zones?
A: JAR/FAR 25.1195 compliance mandates specific fire suppression requirements for designated fire zones, including two discharges with adequate agent concentration in each zone. This ensures redundancy and effectiveness in controlling or extinguishing fires during emergencies.
Q: How does the power source for fire extinguishing bottles differ for Bottle 1 and Bottle 2?
A: Squibs for Bottle 1 are powered by the Hot Bat Busses, while squibs for Bottle 2 are powered by DC2. In some situations, only Bottle 1 is available for use, which might not comply with JAR/FAR 25.1195.
Q: Why is it mandatory to have the APU running before shutting down Engine 2 on A320ceo family aircraft?
A: The APU ensures a continuous electrical supply to fire extinguishing Bottle 2, which is crucial for compliance with JAR/FAR 25.1195. This requirement enhances safety during engine fires.
Q: What is SETWA, and how does it address the power supply issue for Bottle 2?
A: SETWA, or Single Engine Taxi Without APU, is a wiring modification that maintains electrical supply to Bottle 2 squibs even when the aircraft is operating on ‘Batteries Only.’ This upgrade can be installed relatively quickly and enhances safety during engine fires.
Q: Which aircraft models benefit from the SETWA upgrade, and how does it impact APU requirements during single engine taxi?
A: SETWA is available for A320ceo Family aircraft. By default, A320ceo family aircraft require the APU during single engine taxi. A320neo family aircraft do not need the APU for SET-IN because their wiring is already modified as per SETWA.