GE Aerospace has been a bright light for industrial investors for years, despite hard times for Boeing and Airbus after the pandemic. But like the proverb goes: All good things must come to an end.

On Monday, Melius Research's Scott Mikus essentially said just that when he downgraded GE Aerospace to Hold from Buy.

"Great times don't last forever," wrote the analyst.

The cut dragged shares down 3.3%, to $313, in early trading. The S&P 500 was off 0.6%.

Mikus also downgraded aircraft components makers Honeywell Aerospace, TransDigm, Heico, and Woodward to Hold. All those stocks were down, too.

The aftermarket is the problem ahead. Aerospace companies typically make most of their money on parts and service-not on selling original equipment to jet makers. The aftermarket business has boomed, with fewer new jets from Boeing and Airbus-production was the post-pandemic problem-combined with strong demand for air travel.

But aircraft retirements are slated to tick up to about 3% of the total fleet annually, up from about 2% annually from 2020 to 2025, partly driven by higher fuel costs, which boost the need for efficiency, and manufacturing catch-up from Boeing and Airbus.

A 3% retirement rate-based on planes flying for more than 30 years, which they do-is more normal, according to Mikus. That will translate into marginally less parts and service revenue for aerospace companies as the age of the global commercial jet fleet declines.

To be sure, the changes are dramatic, but aerospace stocks are pricey.

GE shares trade for about 41 times estimated 2026 earnings. The S&P 500 trades for closer to 19 times.

Heico stock trades for about 50 times. Woodward and TransDigm shares trade for 28 and 36 times. Honeywell Aerospace, which recently spun out of Honeywell Technologies, trades for 20 times.

Mikus also lowered his price target on GE Aerospace-to $350 from $428, according to FactSet. The average analyst price target for GE Aerospace stock is almost $400.

The other stocks downgraded also got lower price targets.

TransDigm and Heico went to $1,331 and $350, respectively, from $1,475 and $402. The average analyst target prices are $1,516 and $399, respectively.

Woodward and Honeywell Aerospace went to $388 and $190, respectively, from $458 and $216. The average analyst price targets are $446 and $213, respectively.

Overall, all the stocks, except Honeywell Aerospace, remain popular with othe analysts. The average Buy-rating ratio for the four is about 70%. The average Buy-rating ratio for S&P 500 stocks typically ranges from about 55% to 60%. The Buy-rating ratio for Honeywell Aerospace is 44%.

Mikus is early in calling the top of the aerospace cycle. Still, investors have to think about the issues he raised.