Is a child bike seat allowed in flight? [closed]

It varies by airline, which is why commenters indicate you will need to provide that information to receive a concrete answer. To use some local examples, Qantas provides for a variety of infant items which may include child bike seats (they aren't excluded, but you should check explicitly with the airline):

Infant Items

For each infant travelling with an adult, up to three infant items, each weighing up to 32kg, can be carried free of charge including:

• Collapsible stroller or push-chair;
• Collapsible cot or bassinet; and
• Car seat or baby capsule.

The additional allowances apply only on Qantas operated flights with a QF flight number on the ticket.

Virgin Australia has a similar policy:

Infants

Adults accompanying infants are entitled to carry infant special items as checked baggage free of charge on Virgin Australia domestic flights, irrespective of their combined weight. These items include, but are not restricted to the following:

• Pram/stroller
• Portable cot
• Car seat
• Baby capsule

If the adult does not have a baggage allowance the above items can still be checked in free of charge. Other infant items, such as clothing and toys, form part of the adult's baggage allowance.

As such both would probably allow a child bike seat to be included as free checked luggage, but it's not explicit.

However without a doubt other airlines will differ, depending upon their country/region (US vs European vs Middle East, etc), service status (full service would be more likely to provide for baggage allowances like the above, whereas budget services would be less likely) and domestic vs international flights.