multiple rows with the same maximum value
Yours appears to be a "greatest N per group" problem. What you can do is get the maximum seats per engine results:

SELECT
  engines,
  MAX(seats) AS max_seats
FROM
  planes
GROUP BY
  engines


and, using them as a derived table, join them back to the source to get the rows matching the maximums:

SELECT
  p.engines,
  p.manufacturer,
  p.model,
  es.max_seats
FROM
  planes AS p
  INNER JOIN
  (
    SELECT
      engines,
      MAX(seats) AS max_seats
    FROM
      planes
    GROUP BY
      engines
  ) AS es
  ON p.engines = es.engines
  AND p.seats = es.max_seats
;