Replaces the text on page iii with the text on page iii in ISO 1151-5. Adds the following sub-clause immediately after sub-clause 2.4: 2.5 "Quantities related to energy". The quantities defined are related to the energy of the aircraft with respect to the Earth. The zero level of the potential energy is chosen arbitrarily as the geopotential altitude. The total flight-path climb speed and the total flight-climb angle are directly accessible by flight measurements. The total flight-path altitude results from an integration of the total flight-path climb speed.