RE HARMONIC VIBRATIONS
mseyfang POSTULATED that perhaps some sort of flutter issue may have led to instant disintegration.
Theoretically possible- but not probable.
Flutter testing is standard in the industry, and FBW can automatically reduce such possibilities.
Since the Electra, flutter has become a well understood and well tested aspect of the aircraft certification process. Designers are capable of specifying proper mass balance of control surfaces. The experimental flight test process verifies that the product is flutter free throughout the envelope, and beyond Vmo & Mmo.
If anyone wants to learn more about Boeing's activity in this area on all of its jet airliner models,
. It is a well written history of flight testing of B47, B52, 367-80, 707, 727, 737, 747, 757, & 767 aircraft. The T7 had similar testing. It also discusses flight test anomalies that have not been widely published, such as the deep stall of the T-tail 727, asymmetric and unintended slat deployment on the 737 at speed above Vmo, and another leading edge surprise on the 767. If you understand what the aircraft you fly have been through before you get in them, you will know that MH370 did not break up inflight without some extraneous catastrophic event. The anomalies were addressed with design fixes prior to their being placed in airline operation.