Battery cooling liquid cap missing during pre-flight

aircraft-velisbulletin-historicpriority-hightopic-checklisttopic-incidenttopic-maintenance

Coolant low; filler cap not installed. Until further notice, pilots may not refill coolant themselves — call maintenance.

Background

During pre-flight inspection, the battery coolant liquid was low. This was visible on the sightglass behind the rear battery. When attempting to add cooling liquid, it was found that the filler cap was not installed. The PIB board stated the aircraft was 'leaking some coolant' (logged 17 May 2025), but there was no record of coolant filling activity. Maintenance was alerted, found the filler cap, refilled the coolant, reinstalled the cap, and inspected the aircraft before releasing it back to service.

Maintenance has stated that pilots need a short training on how to service the aircraft.

Key points

  • Pre-flight inspection must include the coolant sightglass behind the rear battery
  • Missing/loose filler caps are a known failure mode
  • PIB notes about leaks must be taken seriously and investigated, not just noted
  • No DIY coolant refills until training is provided

    • Required actions

  • Check coolant level on every pre-flight via the rear sightglass
  • Inspect the filler cap visually — must be present and seated
  • If coolant is low: do not fly, do not refill, contact maintenance
  • Read PIB notes carefully before every flight — they're there for a reason

    • Further reading

    Questions about coolant or PIB? Email maintenance or