General Electric received a big upgrade from Morgan Stanley, but its turnaround hinges on its most important aviation customer, CNBC's Jim Cramer said Thursday.

"GE is a total winner unless — unless — Boeing fails to get this darned plane certified," the "Mad Money" host said. "GE's among the many aerospace suppliers who won't be able to make their numbers unless the 737 Max goes back into being sold and resumes production."

Morgan Stanley raised its rating of the challenged industrial giant to overweight from equal weight, citing a "budding turnaround." The stock rose 3.5% during the session.

Boeing CEO David Calhoun earlier this week said the soonest that the grounded 737 Max planes would return to the sky is June or July. The airplane manufacturer must get clearance from the Federal Aviation Administration for the 737 Max to fly again, after being grounded nearly a year ago for software issues connected to two deadly accidents.

GE's aviation division is an engine supplier to Boeing. Earlier this month, Boeing said it lost orders for 87 commercial airplanes. Not only are Boeing's woes weighing on GE and the airline industry, the Trump administration said it could stunt U.S. economic growth this year by half a point.

"Now, I hope that Boeing's practicing UPOD — under promise and over deliver — with that new deadline. Everybody seems to have a high opinion of David Calhoun, Boeing's new CEO ... so I'm hoping he'll get it right."