English: 10-1438 Mignet HM290 Pou-Du-Ciel Replica. In the 1930s, many Fleas crashed when pilots could not recover from shallow dives, resulting in some deaths. As a result, Flying Fleas were grounded and even banned from flight permanently in some countries. In the United Kingdom, restrictions were placed on Flying Fleas, following a fatal crash on 4 May 1936 at an air display at Penshurst Airfield, Kent.

When on approach to land, the pilot would push the stick forward to gain speed for the flare and landing. As speed built up, the rear wing, operating at a greater angle of attack would gain lift and pitch the aircraft's nose further downward. The pilot's normal reaction would be to pull back on the stick. This action would increase the angle of attack on the front wing by lowering the trailing edge of the wing. Because the trailing edge of the front wing was close to the leading edge of the rear wing, the front wing's downwash would accelerate the air over the rear wing and cause it to gain lift more quickly that the front wing, resulting in an ever increasing nose pitch-down and flight directly into the ground.

Mignet had not encountered this problem during his testing of his prototype, because he could not afford a large horsepower engine. When builders started putting larger engines on them and expanding the flight envelope, the wing interference problem surfaced.

The Royal Aircraft Establishment in the United Kingdom and the French Air Ministry conducted full-scale wind tunnel tests, and discovered the problem. Their investigations resulted in changes to the airfoil used and the spacing of the wings to prevent aerodynamic interference. Later Mignet Flea designs incorporated these changes.

By 1939, there were many improved Flying Fleas in the air, but the aircraft never completely overcame its dangerous reputation - Day 2 Watts Bridge Airfield Festival of Flight 'The Vintage Experience' 2010. File: 10-1438_YWSG_20100829_3434