From Northwest's site:
Size of Luggage
Fee (USD) per Piece
62 inches or less
Free
63 - 160 inches
$80.00
Over 160 inches
Not accepted
And the more worriesome:
Bicycles Northwest accepts non-motorized touring, racing or tandem bicycles as checked luggage only. A bicycle is not included in a customer's free luggage allowance. Northwest only accepts bicycles weighing 100 pounds or less. Bicycles over 100 pounds must be sent air freight.
The following charges apply for transportation (each way) per bike between the US, Canada, Mexico, and the Caribbean:
- 1st Bicycle: $80.00 USD
- Additional Bicycles: $180.00 USD
Northwest accepts bicycles only if the handlebars are fixed sideways and the pedals removed or if the handlebars and pedals are wrapped with protective packing material. Northwest recommends bicycles be placed in a bike box.
Northwest only accepts tandem bicycles for travel between the US/Canada/Puerto Rico/Virgin Islands. Tandem bikes are only accepted on 747/D10/757 type aircraft.
Northwest does not accept liability for loss, damage, or delay of bicycles. Excess valuation insurance may not be purchased for transport of bicycles.