Temples that had a Moroni added after dedication fall into 2 groups. Group one consists of the Boston and Sydney temples which were intended to have Angels but could not at first due to legislation or lawsuits. The second group were dedicated exactly as was intended, with no Angel on the spire.
In the second group, with the exception of Idaho Falls and Freiberg, the process of adding a Moroni required removing a portion of the spire to create a natural looking spot for the statue. This means that after Moroni was placed, the temple was actually shorter than without the statue. (Idaho Falls and Freiberg actually made the spire taller.)
Another thing to consider is that the London Temple is about 5 miles (8.05 kilometres) from the airport. This source suggests that a plane on approach will typically be about 1,500 feet (152.4 metres) up at that distance as it approaches. The London temple is only 190 feet (57.91 metres) tall. Even a plane on shallow approach is not going to be that low that far out from the airport.
“How High Up Is A Plane 20 Miles From Touchdown?” airliners.net