Have had an awful time trying to book longhaul london to Australia with a bassinet. Each airline has different size bassinets and max weights. Everthing on internet here and other forums is out of date - inevitable when planes or airline policy changes I guess. So posting some uptodate info I have gathered.
Thai air - Max age 6 months 10kg
virgin - depends on plane - (9kg or 11kg max)
Qantas - up to 11kg (recommend to 8 months as bassinet only 71cm long)
BA up to 14kg
Singapore up to 14 Kg
We decided to book with Singapore airlines- what a mistake............their website is useless. Keeps crashing when trying to search, extremely slow.......will not let you see available seats until passengers details are entered and if no seats together for a family will not let you go back and change flight time or date except by restarting whole search process, names etc again..... We gave up and booked by phone - that took 90 minutes - yes its true, with hopeless call centre. Eventually booked the bassinet and family (2 adults 2 kids) together (they promised or we wouldnt have booked) - but they couldnt give us seat numbers at that time but would allocate them on their system. Next day I tried checking our seat allocation with their 'manage my bookings online' guess what no seats allocated except a bassinet. 4 times we contacted reservations - supervisors, managers etc Finally it emerges that the call centre cannot see the seat plan! cannot allocate seats and can only see if a bassinet is available - not if there are any seats with it for rest of the family. But they kept reassuring me 'you will be together, we make it happen at check in'.
After 2 weeks I finally got hold of someone in customer relations after being continually fobbed off with recorded messages saying that complaints must be written in etc. The truth is that reservation staff cannot and should not promise seats together for a family (but they do). And that seats next to bassinets are not reserved for families with babies but can be booked by anyone online, and since they are bulkhead and perceived as maybe more legroom get booked up quickly leaving no seats for families next to the bassinet. Result, there are not 2 seats left next to a basinet seat for us. Our family will be separated on 4 lengthy flights of 13hrs.
So unless you book a year in advance online you will not be able to sit with your family. Qantas on the other hand do block out seats next to bassinets and then allocate those seats for families and babies when you book by phone.
And when reservations told me 'you will sit together, we make it happen at check in'. Apparently this means maybe someone who booked a bulkhead seat will be bumped out of that seat and others juggled around. Will that happen so our family can sit together we will have to see. And if you are someone who booked a seat next to a bassinet and you dont have a baby start worrying that you may lose that seat.
I'd be interested to hear from anyone who was able to switch seats with passengers sitting next to bassinets or hear if you too were left with family separated on the flight.