ENG23LA033

The loss of both Integrated Drive Generators (IDG) due to worn fixed cylinder block bores, which caused the IDGs to be tripped offline and caused the airplane to enter an emergency electrical configuration.

Information received from JetBlue maintenance and the download of the number 1 generator control unit (GCU) indicated that the number 1 integrated drive generator (IDG) had tripped offline twice over the five days before the incident flight. The digital flight data recorder (DFDR) and GCU data showed that, during the incident flight, the number 1 IDG tripped offline, followed by the number 2 IDG. The loss of both IDGs caused the airplane to enter the emergency electrical configuration and deploy the ram air turbine (RAT). Given the electrical configuration of the airplane at the loss of the number 2 IDG (the APU was not online), the emergency electrical configuration change would cause a temporary loss of the flight deck displays as the electrical system transitioned to power from the RAT. The examination of both the airplane’s IDGs revealed that all of the fixed cylinder block bores were worn beyond tolerance. The IDG manufacturer Collins Aerospace indicated that worn cylinder block bores would make it difficult for an IDG to maintain a constant and consistent frequency; fluctuations in the frequency of the IDG’s output power made it susceptible to faults that could cause the IDG to trip offline.

On August 3, 2023, at 8:35 am eastern daylight time (EDT), JetBlue flight 18, an Airbus A320, registration N649JB, experienced a loss of both engine integrated drive generators (IDG) while on approach to Jacksonville International Airport, Florida. The airplane’s ram air turbine (RAT) deployed automatically. The airplane landed without further incident or injuries reported by any of the occupants. The flight was an IFR flight conducted under 14 Code of Federal Regulations Part 121 from Fort Lauderdale, Florida to Jacksonville, Florida. The airplane departed Fort Lauderdale International Airport (FLL) at about 0745. The takeoff, climb, cruise and descent portions of the flight were completed without incident. At 0833:42, as the airplane was descending through 2,330 feet pressure altitude, the number 1 IDG, connected to engine 1, experienced an over frequency fault and was taken offline by the number 1 generator control unit (GCU). As part of the airplane’s normal electrical system design, the AC BUS 1 electrical system was transferred to the AC BUS 2 system, and the AC BUS 2 system provided electrical power to both systems. At about 0834, the flight crew started configuring the airplane to start the auxiliary power unit (APU). Once it was started and placed online, the APU would have provided an additional electrical power source to AC BUS 2. At about 0834:25, the airplane’s number 2 IDG experienced an over frequency fault, which caused the number 2 GCU to take the number 2 IDG offline. The loss of the second (both) IDG, without the APU powered and online, caused the airplane to enter the emergency electrical configuration. Note: this time is estimated since the ship time is lost due to the loss of the second AC BUS. The airplane’s digital flight data recorder (DFDR) was not powered for approximately 55 seconds; the loss of DFDR data is an indication of an emergency electrical power condition. Electrical Power System Description The airplane’s electrical power system (EPS) consists of a three-phase 115/200 Volt, 400 Hertz (Hz) constant-frequency Alternating Current (AC) system and a 28 V Direct Current (DC) system. The EPS comprises two electrical busses denoted AC BUS 1 (left) and AC BUS 2 (right). There is also a third bus, called the “AC Essential’ (ESS) Bus, which is supplied by either AC BUS 1 or AC BUS 2; the AC ESS BUS supplies power to most of the critical aircraft systems. The EPS system is normally powered by two engine-driven Integrated Drive Generators (IDG), one mounted on each airplane engine. Each generator is driven from the engine high-pressure spool via the engine accessory gearbox and an integrated hydro mechanical speed regulator. The regulator transforms the variable engine rotational speed into a constant-speed drive for the generator. The constant-speed drive and the generator together comprise the IDG. In a normal flight configuration, each IDG supplies power to its own distribution network via its Line Contactor (GLC); the two IDGs are never electrically coupled. The AC BUS 1 and AC BUS 2 networks are designed to be normally independent of one another, so that the failure of one network should not affect 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. Also, the airplane’s DFDR is supplied by AC BUS 2 and the cockpit voice recorder (CVR) is supplied by AC BUS 1 via the AC ESS BUS. The EPS also comprises a third generator (APU GEN) that is driven directly by the Auxiliary Power Unit (APU); it produces the same electrical output as each of the main engine generators. Each IDG is controlled by a Generator Control Unit (GCU). The GCU’s main functions are to control the frequency and voltage of the IDG output and to protect the network by controlling the associated generator line contactor (GLC). The GCUs also monitor the output of their respective IDG. An additional ground and auxiliary power control unit (GAPCU) regulates the frequency and voltage of the APU generator, when powered, and external power, when connected. The flight crew controls the electrical system via the electrical panel, located on the overhead console in the cockpit. This panel provides for annunciation of the status of the electrical systems and fault conditions. The IDG control switches are identified as GEN 1, GEN 2 and APU GEN for the left, right and APU generators respectively. If an IDG fault occurs, an amber fault message will illuminate on the respective generator control push button switch indicating the channel is offline. For an IDG fault, pressing the push button once turns the IDG to OFF. Pressing the push button a second time is required to reset the IDG back to ON. The EPS is designed for automatic reconfiguration with the loss of a single IDG. The EPS will automatically reconfigure so that the remaining IDG will provide power for both systems; the complete network (normal and emergency) remains available and is supplied by the remaining IDG. In this configuration, both the DFDR and CVR continue to be powered. Note: this reconfiguration assumes the APU is not powered. If both IDGs fail or are otherwise taken offline by their respective GCUs, the airplane is designed to revert to the emergency electrical power (EMER ELEC) configuration. In the event of a loss of both the AC BUS 1 and AC BUS 2 busbars in flight, vital services can be fed by an AC 5 kVA Emergency Generator, driven by the Ram Air Turbine (RAT), which is a wind turbine that rotates in the airstream after dropping from the bottom of the fuselage. The RAT deploys automatically because of the loss of both main AC busbars but can be deployed manually by flightcrew selection. RAT deployment is indicated by a green icon on the flight deck display (ECAM) hydraulic system page. In the EMER ELEC configuration, electrical power is removed from the DFDR, but the CVR remains powered. In addition, the transition to the EMER ELEC configuration causes a temporary loss of the flightdeck displays. Integrated Drive Generator Description Inside each IDG, a hydraulic pump and motor assembly provide trim to the gear differential that converts a variable input speed into a constant output speed. Within the pump and motor assembly are two cylinder blocks, one fixed and one variable. Each cylinder block includes nine cylindrical bores with a set of pistons fitted inside each bore. The nine bores and pistons of a newly manufactured cylinder block are matched to meet Collins Aerospace’s (the original equipment manufacturer) specification for tolerance between the bore diameter and piston size. The fixed and variable cylinder blocks work together, using the flow of hydraulic fluid and a governor, to produce a constant output speed. As the hydraulic fluid moves through the rotating cylinder blocks, the pistons move (back and forth) within each of the nine cylinder bores. Over time, the friction caused by the piston movement wears the inside of the bores. When the bore diameter becomes too large (and exceeds Collins’ maximum tolerance), the IDG cylinder block is removed and replaced with a new or repaired cylinder block. The Federal Aviation Administration (FAA) has approved overhaul processes that “resleeve” all the block bores; a new brass bushing (sleeve) is installed inside each of the nine bores (Note: One company that is approved by the FAA to perform the resleeving process, Aircraft Component Repair (ACR), denotes resleeved cylinder blocks by etching “CB31773” into the block exterior). The thickness of the newly installed bushing sleeve decreases the bore diameter back to the original size. Software resident in the GCUs is used to monitor and control the associated IDG and electrical channel. The GCU has the authority to take an IDG offline (trip) if the software monitors detec