Possible to travel undetected, especially by a very experienced pilot.
"Primary radar, which bounces off the skin of the plane, requires line of sight. Malaysian authorities have suggested MH370 flew at very low altitudes - as low as 5000 feet- which could have masked its flight path, particularly in hilly terrain, so a north-west path cannot be ruled out entirely."
Kuala Lumpur: Malaysia Airlines flight MH370 dropped to altitudes as low as 1524 metres (5000 feet) using a dangerous flying technique called “terrain masking” to avoid radar in at least three countries, investigators believe.
Which 3 countries, not too many in the Indian Ocean.....
