\documentclass[a4paper,12pt,fleqn]{article}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\newcommand\eqnmarg[2]{%
  \noindent%
  \begin{minipage}{.99\linewidth}#1\end{minipage}
  \rlap{\hspace{\marginparsep}%
  \begin{minipage}{\marginparwidth}#2\end{minipage}}%
}
\parindent=0pt
\begin{document}
\rule{\linewidth}{1pt}

\eqnmarg{%
\begin{align} 
  &\frac {\sigma_{m,y,d}} {k_m \cdot f_{m,y,d}} 
	 + \frac {\sigma_{c,0,d}}{k_{c,y} \cdot f_{c,0,d}} \leq 1,0 \\[1ex]
  &\text{\rule{1.5cm}{0pt}mit : }\nonumber\\
  &\rule{1.5cm}{0pt}k_{c,y} = min \left( \frac{1}{k + \sqrt{k^{2} - 
		\lambda_{rel,c}^2}} ; 1 \right)
\end{align}}{%
 \tiny foo bar baz foo bar baz foo bar baz 
}
\eqnmarg{%
\begin{align} 
  &\frac {\sigma_{m,y,d}} {k_m \cdot f_{m,y,d}} \\[1ex]
  &\text{\hspace*{1.5cm}mit : }&&\nonumber\\
  &\rule{1.5cm}{0pt}k_{c,y} = min 
\end{align}}{%
 \tiny foo bar baz foo bar baz foo bar baz 
}

\end{document}