DUAS31 - Battery fell out in flight

Initial Report

Our fleet of a certain type of fixed-wing drone does not have consistent battery bay measurements.  This led to me incorrectly fitting the battery to the aircraft, which finally resulted in the battery being dropped from the airframe and a consequent hard landing breaking two rear v-tail elevators.

CHIRP questions and reporter’s answers:

1. Can you confirm that the battery bay size on each aircraft that is built is slightly different, but the battery size is always the same, thus the difficulty in being able to fit the battery correctly?

Answer: Yes, there is slightly more padding in some of our aircraft. The batteries are the same size. The interesting issue is that I was following my own experience of engineering and effectively laying “flat” the battery, which was the orientation most appropriate for the airframe in front of me. However, the battery was setup for fitting to the “upright” orientation.  I was unaware we had two formats of battery bay spacing.

2. Is the battery secured in its position by sticky tape, rather than a more permanent method?

Answer:  The battery is secured (normally) by two separate attachments. One Velcro strap and Velcro underneath the battery so it cannot slip backwards. In this case the Velcro on the floor of the airframe battery bay was not able to attach to the Velcro on the battery because it had been rotated to the side.

3. Did the battery dislodge as part of a landing sequence, or did it happen when you were inverted?

Answer:  Landing and go-around. We don’t fly inverted.

4. Are there other build-quality issues that also have an impact on pilot confidence in the equipment?

Answer:  There are no other issues at present, and build standards are being addressed internally.

5. Have your comments as the pilot been accepted internally and fed back into the Safety Management System in the appropriate manner?

Answer:  Yes.

Lessons learned:

As an organisation we need to improve the consistency of the build-standard of the same type of aircraft.  This will enable our RPICs to have confidence in the required on site assembly across that fleet and ensure safer operating of the flight.

CHIRP Comment

There are a few points worth emphasising from this report:

• Manufacturing an aircraft that has several different ways of fitting the battery, but no outward indication that helps the pilot tell which version it is, will almost certainly lead to confusion and eventually a battery being incorrectly fitted. Whilst it sounds as if this has now been addressed, it is something of a classic problem. There may well of course be an underlying reason we are not aware of, but consistency in manufacturing tolerance at the point of construction, and then later when performing the initial pre-flight checks, is always a plus.
• It seems that there was no manual explaining how you fit the battery either in the controller or in a physical printed format that the pilot was following which might have alerted them to the different installation alternatives. If there had been it would undoubtedly have helped.
• There is no mention of training in the report, but on the assumption that there was training on this particular aircraft, perhaps the alternative battery installation formats should have been highlighted and made clear in training material and the Operators Manual. In particular if incorrect fitting was likely to result in movement of the centre of gravity, which is what looks like happened in this occurrence, an emphasis on what the outcome of incorrect fitting could be, might have helped the pilot remember how important it was to fit the battery correctly.

Ultimately it is the pilot’s responsibility to ensure the battery in the aircraft that is about to fly is secured in the correct way so, if there’s any doubt, then there’s no doubt, ask someone to clarify anything that you’re unsure of before you operate your equipment.