getting to grips with aircraft performance 如何掌握飞机性能 2

The last condition is generally achieved by portable oxygen. As a result, the following table (D2) summarizes the passenger oxygen requirement :

Table D2: Passenger Oxygen Supply Requirement
3.1.3. Flight Profile
3.1.3.1. Oxygen system limitation
Following a cabin pressurization failure, the cabin pressure altitude shall be considered the same as the aircraft’s pressure altitude, unless it can be demonstrated that it is highly unlikely. In the studies, it is always assumed that the cabin pressure altitude is the same as the aircraft’s pressure altitude.
As a result, it is possible to establish a flight profile, with which the aircraft must always remain, taking into account the above-mentioned oxygen requirements. This profile depends on the installed oxygen system:
.  
Chemical system: Fixed profile (published in the FCOM).

.  
Gaseous system: Customized profile (depends on the number of oxygen bottles and obstacle location).

This flight profile represents the maximum level that can be flown with respect to the oxygen system’s capability. As an example, the following Figure (D13) shows the descent profile of a 22 minute oxygen system.

For example, the above profile shows that 7 minutes after the cabin depressurization, the aircraft must fly at or below FL250.

3.1.3.2. Performance limitation
The above descent profile only depends on the oxygen system’s capability, and not on the aircraft’s performance capability.
Nevertheless, this doesn’t mean that the aircraft is always able to follow the oxygen profile, particularly in descent. As a consequence, the performance profile must be established, and this profile must always remain below the oxygen profile. The calculation is based on the following assumptions:
.  
Descent phase: Emergency descent at MMO/VMO. Airbrakes can be extended to increase the rate of descent, if necessary.

.  
Cruise phase: Cruise at maximum speed (limited to VMO).

As a result, for a given initial weight and flight level, the oxygen profile, function of the time, is transformed into a performance profile, function of the distance (Figure D14).

Note: When establishing this performance profile, it is always assumed that the aircraft is able to fly at MMO/VMO. Cases where speed should be decreased (structural damage, turbulence…) have not to be taken into account.

3.1.4. Minimum Flight Altitudes

The minimum flight altitudes must be selected as follows:

“FAR 121.657
(c)
No person may operate an aircraft under IFR, […] in designated mountainous areas, at an altitude less than 2,000 ft above the highest obstacle within a horizontal distance of five miles from the center of the intended course.”

“JAR-OPS 1.250

(a)
An operator shall establish minimum flight altitudes and the methods to determine those altitudes for all route segments to be flown […].
　
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