Observation from message #7, discussing SIGHT-signals vs VOICE-comm, during RAMP ground-handling:
"... using hand signals ... don't agree that ... unsafe ... Hand signals don't have a language barrier and are clear and concise...."
Maybe a better judgment of "safety" -- on the usefulness of SIGHT-signals during RAMP ground-handling -- would be to ask the victim, or the witnesses, after a mishap. Here's this mishap-pilot's conclusion, from his report:
The captain reported,
"Flight two hours late ... pushback with no headphone. Last hand signal seen to start engines, ... went under nose. .... Tug driver signal a problem, shut down engine. ... leg stuck under nose gear. Coordinated ... push aircraft back. ... taken to hospital. ... Problem would have been avoided with working headset ..."
Note, that the choice to push-back WITHOUT voice-comm was taken with the LATE departure. Other times, the choice to NOT use VOICE-headset is a sudden decision, with no chance to review /agree on SIGHT-signals. Other ramp mishaps show that pilots don't look 100% OUTSIDE at the signal-man, but rather pilots get busy with other inside tasks during pushback.
The problem has been the mish-mash of odd-cases, that the pilots could not anticipate. Without information (communication), pilots are INSIDE & without insight to their own mishap. These injuries are the odd "struck-by" mishaps, or "rolling-wheels" cases, amputations, and blunt-force damage. The pilots are mostly third-party, sometimes pilots had no view of the injury-event.
[Maybe everyone should agree the the PILOT will be the "accountable executive", and the PILOT should answer for any injury during pushback. After all, sometimes the pilot is the only licensed-airman involved in the pushback.]
One thing everyone agrees upon: The PILOTS, inside their cockpit, were never exposed to any physical risk. But even so, in one fatal case, a pilot -witness told me that both guys had wished that they had not continued with their flight: just observing the human impacted by the baggage-cart was the beginning a traumatic sequence of errs, with a downed mechanic on the concrete.
On the other side of the choice, over use of HEADSETs during pushback, is the added risk -- expressed in NTSB Recommendation
A-93-55 (the risk to the "walker" on a four-man push crew).