A method for managing a premature descent envelope during a gliding descent of an aircraft to a runway, the method comprising: receiving glideslope deviation data of the deviation of the aircraft from a designated glide path to the runway by an instrument landing system, ILS, onboard the aircraft; receiving localizer deviation data of the deviation of the aircraft from the runway centreline by the ILS; comparing, by the ILS, the glideslope deviation data to an acceptable band of glideslope deviation values and the localizer deviation data to a second acceptable band of localizer deviation values; and when the glideslope deviation data is within the acceptable band and when the localizer deviation data is within the second acceptable band, determining that the aircraft is flying according to horizontal guidance and vertical guidance provided by the ILS; and accommodating a potentially false glideslope signal, by: expanding, by a terrain awareness and warning system, TAWS, the premature descent envelope to produce an increased premature descent envelope for the aircraft, wherein the premature descent envelope comprises a set of minimum clearance altitudes for the aircraft at particular distances from the runway, wherein the increased premature descent envelope comprises a second set of increased minimum clearance altitudes at the particular distances from the runway, and wherein the increased minimum clearance altitudes comprise higher altitude values than the minimum clearance altitudes; and when the aircraft flies below one of the increased minimum clearance values, generating an alert. receiving glideslope deviation data of the deviation of the aircraft from a designated glide path to the runway by an instrument landing system, ILS, onboard the aircraft; receiving localizer deviation data of the deviation of the aircraft from the runway centreline by the ILS; comparing, by the ILS, the glideslope deviation data to an acceptable band of glideslope deviation values and the localizer deviation data to a second acceptable band of localizer deviation values; and when the glideslope deviation data is within the acceptable band and when the localizer deviation data is within the second acceptable band, determining that the aircraft is flying according to horizontal guidance and vertical guidance provided by the ILS; and accommodating a potentially false glideslope signal, by: expanding, by a terrain awareness and warning system, TAWS, the premature descent envelope to produce an increased premature descent envelope for the aircraft, wherein the premature descent envelope comprises a set of minimum clearance altitudes for the aircraft at particular distances from the runway, wherein the increased premature descent envelope comprises a second set of increased minimum clearance altitudes at the particular distances from the runway, and wherein the increased minimum clearance altitudes comprise higher altitude values than the minimum clearance altitudes; and when the aircraft flies below one of the increased minimum clearance values, generating an alert. expanding, by a terrain awareness and warning system, TAWS, the premature descent envelope to produce an increased premature descent envelope for the aircraft, wherein the premature descent envelope comprises a set of minimum clearance altitudes for the aircraft at particular distances from the runway, wherein the increased premature descent envelope comprises a second set of increased minimum clearance altitudes at the particular distances from the runway, and wherein the increased minimum clearance altitudes comprise higher altitude values than the minimum clearance altitudes; and when the aircraft flies below one of the increased minimum clearance values, generating an alert.