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Safety 1st onBoard 35 FLX

The Safety 1st onBoard 35 FLX rear-faces up to 35 lb and has an expiration of 8 years, per Safety 1st.

Previous generationA newer version is out. Some stores still sell this one new. Replaced by Safety 1st OnBoard FLX.

  • 35 lbRear-facing to
See it on Safety 1st's site

When does it expire?

All infant car seats

onBoard 35 FLX: key facts

  • The Safety 1st onBoard 35 FLX rear-faces from 4 to 35 lb and up to 32 in tall, per Safety 1st.
  • Outgrown by height: "The top of your child's head must be at least 1 in. (2.5 cm) below the top of the car seat."
  • It installs with LATCH lower anchor belt (with base), vehicle belt (with base) or vehicle belt (without base).
  • Safety 1st says it expires 8 years after the date of manufacture.
  • Safety 1st lists it as certified for aircraft ("This restraint is certified for aircraft use.").

From Safety 1st's manual and published specs. Always follow the limits on your seat's labels.

How the onBoard 35 FLX stacks up

Against the 74 infant car seats we track. The shaded band is where the middle half of them fall; the dot is this one.

Expiration8 years

Within the typical range for infant car seats (6 years to 8 years).

This one
6 yearsmiddle 7 years10 years
Rear-facing limit35 lbHighest rear-facing limit of 73 infant car seats

Above the 30 lb most infant car seats list.

This one
22 lbmiddle 30 lb35 lb

onBoard 35 FLX: generations

From each maker's published specs.

What sets the onBoard 35 FLX apart

Measured against the 74 infant car seats we compare, from each maker's published specs.

  • Highest rear-facing limitof the 73 infant car seats with it published: 35 lb

Next to its closest matches

Strollers named with the onBoard 35 FLX

3 strollers on Cribpicks are named with the onBoard 35 FLX in a maker's fit list.

StrollerHow it is listed
Safety 1st Grow and Go Flex 8-in-1Named by Safety 1st
Safety 1st Grow and Go Sprint 6-in-1Named by Safety 1st
Safety 1st Turn and Go 360 Rotating ModularNamed by Safety 1st

Matched by brand and model name. Fit can depend on the model year, so check yours with both makers.

Flying with the onBoard 35 FLX

Safety 1st's label: “This restraint is certified for aircraft use.”

What airlines say about car seats:

  • American: “Each ticketed customer is allowed 1 stroller and 1 car seat to be checked free of charge” “If an unoccupied, adjoining seat is not available, the gate agent will check the safety seat to your final destination.” Source
  • Alaska: “We will transport your child's car seat and stroller free of charge as checked baggage.” Source
  • JetBlue: “Checking a child safety seat will not count towards your checked baggage allowance and there is no fee assessed” Source
  • Spirit: “One (1) car seat will be accepted per child as checked baggage at no charge.” Source
  • Frontier: “strollers and car seats can be checked for free.” Source
  • Allegiant: “There is no charge for checking or gate checking one car seat per fare-paying passenger.” Source
  • Breeze: “Child seats may be carried on board the aircraft if a seat has been purchased for the Infant or Child” Source

Quoted from each airline's page as of 2026-11-02.

Where to buy the onBoard 35 FLX

Prices and availability change. We may earn a commission from some links.

good to know
  • Previous generation, still sold by some retailers. Check whether a newer version replaced it.
  • Check for recalls: Search the agency's recall list with the model number and date code from the label: NHTSA recall search.
  • Car seat use and installation: see NHTSA's car seat page, which also lists free car seat inspection by certified technicians. Check the label and the maker's instructions, and ask your pediatrician about your child.

Full specs

Safety 1st onBoard 35 FLX
TypeInfant car seat
Rear-facing weight4–35 lb
Rear-facing heightUp to 32 in
Head ruleThe top of your child's head must be at least 1 in. (2.5 cm) below the top of the car seat.
InstallationLATCH lower anchor belt (with base), vehicle belt (with base), vehicle belt (without base)
Handle in the carCarry handle must be upright and locked when carrying and when installed in the vehicle.
Aircraft labelCertified for aircraft, per the maker
Expires after8 years

Compare the onBoard 35 FLX with

How each closest rival differs from the onBoard 35 FLX, from the makers' specs.

Ask the meadow

onBoard 35 FLX: questions answered

From Safety 1st's published specs, last checked 2026-11-06.

Does the Safety 1st onBoard 35 FLX rear-face longer than other infant seats?

Yes. Its 35 lb rear-facing limit is the highest of the 97 infant seats we track, tied with 22.

Can you use the Safety 1st onBoard 35 FLX in a taxi or Uber without the base?

Yes. Safety 1st lists a baseless install with the vehicle belt; see the manual for the belt routing.

Can you bring the Safety 1st onBoard 35 FLX on a plane?

Yes, Safety 1st lists it as certified for aircraft; look for the red-lettered label that says so. The FAA asks that a car seat go in a window seat so it doesn't block the aisle, and the crew will look for that label.

Is it OK to buy a used onBoard 35 FLX?

NHTSA publishes guidance on used car seats on its car seat page. Safety 1st lists a lifespan of 8 years from manufacture for this model. Check the label and the maker's instructions, and ask your pediatrician about your child.

Still wondering? Write to us at hello@cribpicks.com and we'll look it up.

More infant car seats

Where these specs come from

Last checked 2026-11-06. Spot something wrong? Tell us. Read our editorial and safety policy and corrections.