It sounds nearly unbelievable, but Boeing did test rockets on the Boeing 727.
Their idea was not as strange as it sounds, and it turned out to be an ingenious answer to a very real problem.
A JATO/RATO option was actually available.
The 727-200, which was obviously much heavier than the shorter 727-100, had the option. Due to their greater weight and identical engines to the -100s, the early 727-200s lacked some power until the 727-200 Advanced, which featured JT8D engines, was introduced.
Only 12 727-200s, which were actually the more potent 727-200 Advanced models, were constructed with the JATO option. Serving a number of high-altitude airports in its network, where the 727-200 as constructed would have had its payload restricted to account for the potential loss of one of the three engines before takeoff, put Mexicana in a unique position.
Wings will produce less lift and jet engines will produce less power at higher elevation airports than at lower elevation airports, especially on hot days. This explains the length of the runways of airports like La Paz, Bolivia.
Twelve 727-200s that Mexicana received overcame this limitation by installing a JATO in the lower aft fuselage, just behind the wings. These planes could be identified by a shallow dorsal fairing in front of the #2 intake, which held some of the air conditioning ducting and rerouted avionics that the JATO provision had displaced.
Boeing gave the aircraft the unofficial designation 727-200/JATO, and the rocket installation was only meant to be used in an emergency when the airplane was departing from a hot, high airport at maximum gross weight.
The aircraft would need to be payload restricted without the JATO in order to handle a need to reach a safe altitude in the event of an engine failure after committing to takeoff. The JATO provision would allowed Mexicana to fly its 727-200s with full loads. Should an engine failure occur beyond V1, the JATO would activate, enabling the heavily loaded aircraft to attain a safe altitude.
Later advancements in the JT8D engine, which included an automatic power reserve (APR), finally rendered the JATO provision obsolete. When one of the engines failed during takeoff, it detected a drop in power and immediately increased the power to the other two engines by a considerable amount.
