How to convert UInt16 to UInt8 in Swift 3?

I want to convert UInt16 to UInt8 array, but am getting the following error message:

'init' is unavailable: use 'withMemoryRebound(to:capacity:_)' to temporarily view memory as another layout-compatible type.

The code:

    let statusByte: UInt8 = UInt8(status)
    let lenghtByte: UInt16 = UInt16(passwordBytes.count)

    var bigEndian = lenghtByte.bigEndian

    let bytePtr = withUnsafePointer(to: &bigEndian) {
        UnsafeBufferPointer<UInt8>(start: UnsafePointer($0), count: MemoryLayout.size(ofValue: bigEndian))
    }