I recommend using the following code. It might seem more complicated, but it certainly does a better and more robust job. It is simply assigning your input and output ranges as SrcRng and DstRng. FIND method for ranges is a good way to check for specific values.
Sub PEC()
Dim SrcRng As Range
Dim DstRng As Range
Dim rcell As Range
Set SrcRng = Range ("AE2:AE26848")
Set DstRng = Range("AO2:AO26848")
Set rcell = SrcRng.Find(what:="A.06", after:=SrcRng.Cells(1, 1), _
LookIn:=xlValues, LookAt:=xlPart, SearchOrder:=xlByRows, _
SearchDirection:=xlNext, MatchCase:=False)
If Not rcell Is Nothing Then
DstRng.Value = 1
End If
End Sub