Twin Engine Corporate Captain reported there is no Warning' flag or indication; in this particular model navigation system; if the Glide Path or Glide Slope do not capture during the approach.

Narrative

This is a general report on an anomaly that may occur in all WAAS GPS units that; I believe; should be addressed. After some 35 years flying the 'Steam gauges' in GA aircraft and airliners I have transitioned to state of the art GPS based navigation with the new equipment in Aircraft X. When flying satellite based approaches with WAAS augmented vertical nav there is no warning should the vertical nav feature fail or if the parameters; whatever they may be; are not met. There is no 'flag'. Sometime during the approach a 'NO GP' may appear but with the equipment that we have; dual GTN 750 txi's; it appears much too late in the approach. To be safe the 'NO GP' warning should appear when the approach is selected and the equipment cannot provide vertical path guidance. I have one unit that presents glidepath information as soon as the approach is selected. On the second unit there is no glide path information at all. Good or bad. Both units have the same current data bases. But again; the unsafe situation is the failure of the unit to produce a 'flag' or warning that vertical guidance; for whatever reason; is not available.