Drones carrying lab samples between hospitals in Switzerland have been grounded after a crash 50 yards from where pre-school children were playing.
The drone crashed in woodland after a rope holding its emergency parachute broke, in May, IEEE Spectrum reported.
Swiss Post said it would examine all safety procedures before flights resumed and asked drone-maker Matternet to urgently fix a series of issues.
In January, another of the drones made an emergency landing in Lake Zurich.
In that case, the emergency parachute deployed correctly.
Swiss Post told BBC News: "Safety is our top priority. That's why Swiss Post is now establishing an expert council. It will examine all processes relating to the risk and safety management of drone flights.
"In due course, we will provide more information on this process, the measures implemented and the resumption of flights.
"We rely on Matternet, as our technology partner, and expect the security mechanisms to function."
Swiss Post has asked the Silicon Valley start-up to:
- reinforce the parachute ropes with metal braiding
- have two ropes instead of one
- make a whistle alerting people to its presence louder
Matternet said: "This is the first time we had a failure on the vehicle's parachute system. We had never seen a failure like that in the past, neither in our expansive testing nor in commercial operations.
"At Matternet we take the safety of our technology and operations extremely seriously. A failure of the parachute system is a clear failure of our safely mechanisms and we are taking all the appropriate measures to address it.
"We will restart operations once Matternet and Swiss Post, FOCA [the Federal Office of Civil Aviation] and our hospital customers in Switzerland are satisfied that the appropriate mitigations have been applied."
Swiss Post began trials of laboratory samples being carried by drone back in 2017 and so far has carried out about 3,000 successful flights.