MDA’s Canadian Ownership Strengthened As Ontario Teachers’ Pension Plan Makes Major Investment

Richmond, B.C. – MacDonald, Dettwiler and Associates Ltd. (TSE: MDA) reports that Orbital
Sciences Corporation of Dulles, Virginia has agreed to sell 12.35 million of its 18 million shares
in MDA to a group of primarily Canadian institutional investors in a private transaction. The
group includes the Ontario Teachers’ Pension Plan, the BC Investment Management
Corporation, and CAI Capital Partners and Company II, L.P.

It is anticipated that the transaction will be completed in early May 2001. This transaction will
make MDA a more widely held Canadian public company.

The share sale includes an option to buy the remaining Orbital holdings in MDA by May 31st.

“This is a very positive development for our company,” said MDA President and CEO Daniel
Friedmann. “It significantly increases MDA’s Canadian ownership, diversifies shareholdings,
and will lead to increased liquidity.”

Headquartered in British Columbia, MDA employs 1800 people around the world, and provides
essential information for decision making in the workplace.

Related web sites:
www.mda.ca
www.orbital.com
www.otpp.com

For more information, please contact:

Ted Schellenberg
Media Relations
MacDonald Dettwiler
Telephone: (604) 231-2215
E-mail: teds@mda.ca