Investigators examining a Croatia Airlines Bombardier Q400, which landed with its nose-gear retracted at Zurich, believe a fractured sensor cover obstructed the nose wheel.

While the inquiry into the 27 September landing is yet to conclude, preliminary checks by Swiss accident investigation authority BFU found a cover plate, which protects weight-on-wheel sensors, had broken at its attachment lugs.

It had pivoted upwards and was squeezed between the nose-gear’s upper and lower drag struts. BFU says the cover plate “did impede” the nose-gear extension.

After the Q400 had been recovered from the runway, investigators attempted to lower the nose-gear with the alternate release handle. The force required was 543N.

Once the broken cover plate was extracted, says BFU, the nose-gear was cycled again using the normal and alternate release mechanisms “without any problems”. It adds that the force needed to activate the alternate release system was 334N, a reduction of nearly 40%.

Croatia Q400 nose gear jam