The Boeing 737-400 is a stretched version of the second generation aircraft, created to hold more passengers. This iteration has 3 meter fuselage stretch and now holds 188 people in its maximum configuration. The changes are minor such as an increased tail bumper for protection against over rotation at takeoff due to longer lengths on this model compared with other smaller models like the 300 which only seats 150 comfortably (or 170 uncomfortably). All three second gen iterations share extensive systems/structure commonality – all carrying same type rating for pilots regardless of size!