\begin{tikzpicture}
\begin{axis}[
title={Operation Mode},
ylabel={Mode},
ylabel near ticks,
%ymax=-0.4,
xmax=18,
xmin=0,
width=12cm,height=4cm,
grid
]
\addplot[red,very thick] table[x index=0,y index=5,col sep=space] {data1.txt};
\addlegendentry{mode}
\addlegendimage{1: manipulation}
\addlegendimage{2: navigation}
\end{axis}
\end{tikzpicture}