Meanwhile, Mick from metabunk is now saying the "true air speed" is the value we need and therefore the object couldn't have been a bird.
My calculations used TAS=true air speed. And his last comment there regarding TAS correction seems to be "Indicating the object is flying away from the jet at around 20 knots". Using the TAS speed instead of CAS just reduces the speed of the bird, making it just more likely. I did a similar correction to my earlier more coarse calculations, and the results were similar.
I did some googling for average speeds of an albatross, and here are the first results I found:
"Albatrosses reach average speeds of 36 mph, he said, but dynamic soaring would allow them to fly much faster if the high speeds didn’t cause excessive force on their wings."
A Robotic Albatross?
"Speeds of 50-60 kph were common: one of their birds maintained an average speed of 50 kph over 800 kilometers. (Pierre Jouventin and Henri Weimerskirch working with breeding wanderers at the Crozets, reported 80 kph as the typical average speed of wanderer commuting to its feeding grounds.)"
"Satellite tracking data indicate that wandering albatrosses can cover 15,000 kilometers (9,300 miles) between visits to feed their chicks, reaching speeds of 80 kilometers (50 miles) per hour. High speeds over long distances are their specialty. One bird was observed to travel 808 kilometers (502 miles) at an average speed of 56 kilometers (35 miles) per hour."
Enhanced Essentials of Oceanography
Not a bad match to the average speed of 60 km/h=38 mph I just calculated for Albert .