JEJU AIR 7C2216 CVR and FDR LAST 4 MINUTES RECORDINGS OUT - POSSIBLE EVENT - CROSS BUS TIE RELAY NOT OPENED

 

On the very moment the GLIDE SLOPE is intercepted the CROSS BUS TIE RELAY automatically opens.

 The CROSS BUS TIE RELAY opens to isolate the navigation receivers and Flight Control Computers. The RELAY opening prevents all approach phase data be removed from FDR because of only one electrical failure.

The CROSS BUS TIE RELAY also opens when the BUS TRANSFER switch is moved to OFF.

 If NORMAL power sources to DC BUS fail, the emergency source of DC power is the batteries.

 If both generators come disconnected from the BUS TRANSFER BUS, the AUTOPILOT disengages and it can't be ENGAGED up to the generators are available. The plane must be piloted MANUALLY. It will be hard work.

With no electrical source available, the batteries can supply electrical power up to minimum of 60 minutes.

UPDATED UPON PRELIMINARY REPORT Jan 27, 2025

Cockpit Voice Recorder

The cockpit voice recorder uses four independent channels to record flight deck audio for 30 minutes or 120 minutes. Recordings older than 30 or 120 minutes are automatically erased. One channel records flight deck area conversation using the area microphone. The other channels record individual ACP output (headset) audio and transmissions for the pilots and observer. (Aircraft fit dependent) The RIPS (Recorder Independent Power Supply) provides power to the cockpit voice recorder for 10 minutes after aircraft power is interrupted either by normal shutdown or by any other loss of power. Normal power supply 115V TRANSFER BUS 2 and 28 V from DC BUS 2.

VOICE RECORDER Switch (when fitted):

AUTO - powers the cockpit voice recorder from first engine start until 5 minutes after last engine shutdown

ON - powers the cockpit voice recorder until the first engine start, then trips the switch to AUTO. On aircraft with no switch the voice recorder is active anytime 115V AC is applied to airplane.

As soon as the aircraft has intercepted the LOCALIZER course, following that the pilot attention will be on GLIDE SLOPE interception.

BATTERY POWER

Emergency source for:

- Static Inverter/AC Standby Bus

- DC Standby Bus

- Battery Bus

- Hot Battery Bus

- Switched Hot Battery Bus

The Static Inverter changes 24 DC power to 115 AC power for the AC STANDBY BUS.

The HOT BATTERY BUS is always connected to the battery, and all its components operate as long as the battery voltage is above a minimum value.

The pilot must move the BUS TRANSFER switch to OFF position and turn off the HIDRAULICS ELECTRIC PUMPS.

After trying to restore the generators, if both GEN OFF BUS (L & R) lights stay ON, the pilot must land the plane ASAP.

The CVR is a customer option, popular choices are the L-3 FA2100 and Honeywell 980-6020/980-6022. Both manufacturers offer these with a crash survivable memory unit (CSMU) for protection of the solid state voice recording memory. The capacity of the CSMU is a customer option, legally the state of registration may only need 30 minutes. The CSMU retains the most recent 30 or 120 minutes of audio, digital, and timing information. Unless you know the part number of the CVR installed, you will not know if it is a 30 minute or 120 minutes capacity, they look identical.

Another customer option is the overhead "Voice Recorder" switch, with ON and AUTO positions. If it has that switch it should shut down 5 minutes after the engines are shut down (based upon oil pressure), if it does not have that optional auto switch it can record whenever 115V is supplied.