The flight log cannot be written

What ArduPilot says:

• PreArm: No SD card
• PreArm: Logging failed

Logging is on (LOG_BACKEND_TYPE) and the logger says it cannot write. With an SD card: opening a log file failed within the last 5 seconds, the last write failed, or the logging thread has stopped. With a flash chip: it was not found or is full. ArduPilot will not fly without the log you would need after a crash. A missing card normally shows as “Logging failed”, because that test comes first; “No SD card” means the same.

What to do, most likely first

1. There is no SD card, or it is not pushed in all the way.

   FixInsert a card and reboot.

2. The card cannot be read or written: wrong format, worn out, or a fake.

   CheckPut it in a computer: there should be an APM folder with a LOGS folder in it, and the newest files should open.

   FixFormat it as FAT32 on a computer, or replace it with a good brand-name card of 32 GB or less. If a good card fails only on this board, try BRD_SD_SLOWDOWN 1 or 2.

3. LOG_BACKEND_TYPE asks for logging over MAVLink, and no ground station is taking the log.

   FixSet LOG_BACKEND_TYPE to your board's default: 1 for an SD card, 4 for a flash chip.

4. The board logs to a flash chip, and it is full.

   FixDownload the logs you want to keep, then erase them all from the ground station's log screen.

With LOG_DISARMED 0 (the default) nothing is written before arming, so a missing card is often noticed only at that moment, as “Arm: Logging not started”.

Parameters to look at

Where to do it:Setup & Tuning Guide