$900-Million Aircraft Order: Midway Airlines has announced the largest order in its 10-year history--29 firm orders for McDonnell Douglas MD-82 twin-jets with options for an additional 37. Meanwhile, the airline accepted the first two of eight MD-87s it has on order. The total estimated value of the 37 MD-82s and MD-87s is more than $900 million. Delivery of the first four MD-82s is scheduled for 1990, with the rest of the deliveries to continue through 1993. The options are planned for delivery beginning in 1993 and continuing through 1997. The order, including the purchase options, has a total value of about $1.8 billion.