N521NK

HISTORY OF FLIGHTOn February 15, 2020, at about 7:42 AM pacific standard time (PST), Spirit Airlines Flight 1818, an Airbus A319-132, N521NK, experienced a fault with both engine integrated drive generators (IDG) while on approach to the Sacramento International Airport (SMF), Sacramento, California.

According to the flight crew, while the airplane was descending from 4,000 feet to 2,000 feet during their approach into SMF, they heard a “clicking noise” behind the captain’s seat that sounded like an electrical component or contactor opening or closing. They also observed the “ELEC GEN 2 FAULT” message on the lower Electronic Centralized Aircraft Monitor (ECAM) and a FAULT caption illuminate on the overhead panel. Within about 11 seconds, they heard another “clicking noise” and observed the “ELEC GEN 1 FAULT” message appear on the lower ECAM. These faults resulted in the loss of electrical power supplied to both electrical networks (AC BUS 1 and AC BUS 2) leading to the loss of several flight deck displays and systems. Upon the dual loss of power, the ram air turbine (RAT) automatically extended and began driving the emergency generator to provide electrical power to vital services.

Due to the nature of the emergency and the phase of flight, the flight crew declared an emergency and asked for an immediate visual approach to runway 34L. The aircraft landed without incident, was met by fire trucks, and safely towed to the gate where the passengers were deplaned normally. None of the 117 occupants aboard the airplane were injured. The regularly scheduled passenger flight was operating under the provisions of Title 14 Code of Federal Regulations Part 121 from the McCarran International Airport (LAS), Las Vegas, Nevada to SMF.

AIRCRAFT INFORMATIONThe Airbus A319, in common with other Airbus aircraft, is equipped with an electronic instrument system (EIS). This system consists of six liquid crystal cockpit display units (DU), two displays in front of each pilot and two central displays. The upper display is the Engine and Warning Display (E/WD), the lower display is the Systems display. The pilot displays are part of the electronic flight instrument system (EFIS) and provide primary flight instrumentation information on the primary flight display (PFD) and the navigation display (ND). The PFDs present information on aircraft attitude, performance, flight path and autopilot modes and the NDs provide navigation, weather radar and Traffic alert and Collision Avoidance System (TCAS) information.

The System Display (SD) has the capability to display 13 different system pages, the cruise page or the status page. The display has two areas: the upper section of the screen provides information based on the selection of the display, and the lower section contains permanent data that is always present regardless of the page selection. This permanent data contains information on the total and static outside air temperatures, the time, the aircraft’s gross weight and its center of gravity. In flight, the ‘default’ cruise page is generally displayed. This page shows additional engine parameters, such as fuel burn, oil quantity and vibration levels, as well as cabin air and pressurization parameters.

The lower ECAM display unit normally provides the “System Display”, which presents synoptic diagrams showing the status of various aircraft systems. The ECAM display is controlled through the ECAM Control Panel (ECP), located on the center pedestal directly below the ECAM displays.

A specific system page such as the “ELEC System” may be called up manually, by selection of the appropriate button on ECP; a page will appear automatically following an aircraft system failure.

For both the synoptic diagrams and the control panel captions, normal system conditions are displayed in green or white and abnormal conditions in amber. A number of fault conditions also cause the red Master Warning or amber Master Caution caption lights on the flight deck to illuminate and a continuous or single chime to sound.

The electrical power system (EPS) on this aircraft consists of a three-phase 115/200 V 400 Hz constant-frequency AC system and a 28 V DC system. The EPS comprises two electrical networks, a left and a right, denoted AC BUS 1 and AC BUS 2. There is also a third network, called the “AC Essential” Bus, which is supplied by either AC BUS 1 or AC BUS 2; this BUS supplies power to most of the critical aircraft systems.

AC BUS 1 and AC BUS 2 networks are normally independent of one another, so that the failure of one network should not affect the operation of the other. The power supplies for flight critical systems are for the most part segregated, so that the loss of a single power source should not cause concurrent failures of systems necessary for continued safe flight.

Two enginedriven AC generators (GEN 1 & GEN 2), one mounted on each engine, normally power the EPS system. Each generator is driven from the engine high-pressure spool via an engine accessory gearbox and an integrated hydro-mechanical speed regulator. The regulator transforms variable engine rotational speed into a constant-speed drive for the generator. The constant-speed drive and the generator together form an assembly known as an Integrated Drive Generator (IDG). According to Spirit Airlines records, the Number 1 IDG (IDG1) was installed on the aircraft on November 12, 2017, in Philadelphia, PA. It had been installed for approximately 827 days and accumulated 8,582 hours and 3,693 cycles prior to its removal. The Number 2 IDG (IDG2) was installed on the incident aircraft on March 29, 2017, in Orlando, FL. It had been installed for approximately 1,055 days and accumulated 10,584 hours and 4,581 cycles prior to its removal.

The output frequency and voltage of each IDG is controlled by its respective generator control units (GCU); the Number 1 GCU controls the IDG1 and the Number 2 GCU controls the IDG2. The GCUs also protect the network by controlling the associated generator line contactor (GLC).

The EPS also comprises a third generator (APU GEN) that is driven directly by the Auxiliary Power Unit; it produces the same electrical output as each of the main engine generators. Additionally, a ground power connector near the nosewheel allows ground power to be supplied to all busbars. A Ground and Auxiliary Power Control Unit (GAPCU) regulates the frequency and voltage of the APU generator; it also protects the network by controlling the external power contactor and the APU generator line contactor.

In the event there is a loss of both the AC BUS 1 and AC BUS 2 busbars in flight, vital aircraft electrical services can be supplied by an Emergency Generator which is driven by the ram air turbine (RAT). The RAT deploys either automatically, usually because of loss of both main AC busbars, or on manual selection. RAT deployment is indicated by a green icon on the ECAM hydraulic system page.

The electrical system is controlled via the electrical panel located on the overhead console in the cockpit. This panel provides for annunciation of the status of the electrical system and fault conditions. The generator control switches are identified as GEN 1, GEN 2 and APU GEN for the left, right and APU generators. If a fault occurs with a generator, an amber fault message will illuminate on the respective generator control push button (PB) switch indicating the channel is offline. For a generator fault, pressing the PB once turns the generator to OFF. Pressing the PB a second time is required to reset the generator back to ON.

A review of maintenance records found that N521NK had experienced a loss of power supplied from IDG1 and IDG2 prior to the February 15th, 2020, flight to SMF. The following paragraphs describe the four previous events. According to Airbus, the introduction section of their troubleshooting manual (TSM) indicates that if the operator cannot find a fault symptom and/or fault isolation procedure necessary to ensure the continued airworthiness of the aircraft, or if the operator thinks that the information given is not complete, they should contact Airbus.

On January 19, 2020, N521NK, operating as Spirit Airlines Flight NK1848, experienced a loss of all electrical power and the loss of nose wheel steering about 3 minutes after shutting down the Number 1 engine while taxing after landing at the Orlando International Airport (MCO), Orlando, Florida. Spirit Airlines Maintenance performed a run-up of the Number 1 engine per the procedures contained in aircraft maintenance manual (AMM) 71-00-00. The full electrical load was supported by IDG1, and no faults were noted. The aircraft was determined to be ok for continued service and no additional troubleshooting was accomplished. According to Airbus, they were not contacted regarding this event.

On January 23, 2020, N521NK, operating as Spirit Airlines Flight NK1445, experienced a loss of IDG1, nose wheel steering and all electrical power during a single engine taxi after landing at MCO. The flight crew observed the ‘ELEC GEN 1 FAULT’ message on the lower ECAM display. Spirit Airlines Maintenance performed an operational test of IDG1 per AMM 24-22-00. No faults were noted. According to Airbus, Using the Airbus AirnavX Troubleshooting tool, TSM task 24-00, “GEN 1 FAULT Warning” could have been used. This task requires the operator to perform an engine run and verify the GEN1 parameters. If the fault is confirmed (i.e. GEN1 parameters are not correct), then the troubleshooting data (TSD) from the GCUs shall be extracted. If the fault cannot be confirmed, Airbus can be contacted.

According to the NVM download from GCU Number 1, N521NK experienced a loss of IDG1 while performing a single engine taxi after landing on January 29, 2020. No maintenance information was available from Spirit regarding this event.

On February 14, 2020, N521NK, operating as Spirit Airlines Flight NK806...