A cabin with good temperature maintenance is important in order to offer passengers a pleasant flight. In modern passenger aircraft, the cabin temperature is regulated by means of the temperature of the feed air which is injected into the cabin.

It is established practice to sub-divide the cabin of the passenger aircraft into several cabin zones, and to supply each cabin zone with air from its own supply line. For this, each cabin zone has its own temperature regulation circuit which regulates the temperature of the feed air in the cabin zone in question in such a way that the ambient temperature in the cabin zone has a required optimum value. In this way, the ambient temperature for each cabin zone can be specially regulated to a target value.

Previously, a single temperature sensor was generally used for each cabin zone. It is generally attempted to position the temperature sensors at points of average heat loading so that the temperature recorded by each respective sensor corresponds to the average in the cabin zone in question. It has been shown that the temperature within a cabin zone is often not even, but it can fluctuate significantly from place to place. Similarly, it is possible to find strong local peaks where the temperature for a passenger is noticeably above or below an average temperature considered to feel pleasant. If a temperature sensor is located at a point of this type of temperature peak, it will give a correspondingly'falsified'signal. This leads to the injected air being either too cold or too hot.

It has also been shown that the temperature distribution within the cabin of an aircraft can depend essentially upon the type and layout of the cabin fittings, ie. the

design of the cabin with regard to seats, toilets, on-board kitchens and similar.

Whereas, of course, different customers often require a totally different cabin design, the location points of the temperature sensors are specified in advance by the aircraft manufacturer. In order to allow a certain degree of flexibility for adaptive measures, in most cases one or two alternative location points are provided. The limited space within an aircraft cabin means, however, that it is impossible to provide a large number of alternative location points. Once a client has expressed his special requirements, it is investigated which of the pre-specified location points is the most suitable. Evidently, a truly suitable location point will not always be found.

Individual adaptation of the sensor location points to the actual cabin design is not normally considered because the cost involved here would be too high.

The aim of the invention, therefore, is to make it possible to offer a higher level of flexibility when choosing the temperature measurement points within the cabin.

The solution to this problem offered by the invention is a system for controlling the temperature of feed air supplied to the cabin area of a passenger aircraft, including - a temperature sensor system by means of which a representative reading can be taken for ambient temperature in the cabin area, and - an evaluation and control unit associated with the temperature sensor system which is provided in order to control the temperature of the feed air dependent upon a deviation of the ambient temperature reading from an ambient temperature optimum value.

In accordance with the invention, it is therefore proposed that the temperature sensor system includes at least one series of sensors positioned along the length of the cabin area, which is activated by an activation signal to give a response signal containing information on temperature at different points along the sensor series.

The sensor series provides location-specific temperature information. By means of appropriate signal evaluation, the preferred temperature for different points (measuring points) along the sensor series can be determined from the response signal without constructive adaptation measures. This creates a high level of flexibility when choosing the measuring points and makes it possible to obtain readings which are constantly representative, independent of the actual cabin design.

Even if there are subsequent changes to the layout of the cabin, the location of the measuring points can be easily adapted. The measuring points can also be specially

chosen dependent upon the seating layout or the flight route, without having to restructure the temperature sensor system.

In accordance with a preferred version, the sensor series is in the form of a fibre optic cable, which is activated by a laser light signal from a laser light source. Fibre optic temperature measurement methods are an established example of this. They use the temperature dependency of certain optical features of the fibre optic cable.

An example of a fibre optic temperature measurement method is a laser radar measuring method based upon the Raman effect. Here, the spectral temperature dependency of a back-scatter signal received in answer to short laser light impulses which are launched in the fibre optic cable is used. The back-scatter spectrum receives a so-called Stokes band and an anti-Stokes band, whereby the spectral intensity of the anti-Stokes band shows a clear temperature dependency. By means of periodical cutting away of individual parts of the back-scatter signal, the temperature can be determined at various points along the sensor series.

It is also possible to use the temperature dependency of the refraction index of a fibre optic cable for location-specific temperature measurement. Rayleigh scatter and the Fresnel effect make it possible to obtain information about the temperature at different points along the fibre optic cable from the reflexion signal received in reply to a laser light impulse.

It should be noted that, within the framework of. the invention, limitation to sensor series in the form of fibre optic cables is in no way intended. Instead of an optical measurement method, electric measurement methods can, for example, also be used, whereby the temperature dependency of electric sizes is used.

The term sensor series'here generally signifies an extended sensor medium in the form of a fibre or a cable. The sensor series can be single-stranded, ie. in the form of a single sensor element, or multi-stranded with two of more sensor elements isolated from one another. A multi-stranded sensor series can include a redundancy so that the whole series doesn't have to be changed if one sensor strand fails.

The invention does not only offer a high level of flexibility with regard to the choice of the location of the measuring points, but also with regard to the number of the same. Thus, in order to regulate the temperature of the feed air injected into a specific cabin area, only the measurement value of a single measuring point has to

be called upon. It is, however, equally possible to obtain individual readings for various points in a specified cabin area using a sensor series, without any additional structural expenditure, and to take an overall measurement value from the individual measurement values. This overall value is then used for the regulation of the feed air injected into the cabin area. The overall value can, for example, be obtained by means of calculation from the individual values measured. In this way, the effect of local and temporary temperature interference can be reduced.

The sensor series is specifically positioned, at least partially, along the length of the aircraft in the cabin area. Particularly with aircraft with a very wide cabin and correspondingly wide rows of seats, the possibility, however, can not be ruled out that significant fluctuations of the cabin temperature may occur, even in the cross direction of the aircraft. It may, therefore be wise to lay the sensor series, at least partially, in the cross direction of the cabin. It is possible, for example, to lay the sensor series as a loop, 26. where the halves of the loop run along opposite sides of the cabin-in relation to a vertical lengthwise average level of the aircraft.

If the aircraft cabin is sub-divided into several cabin zones, each supplied with feed air from its own supply line, the sensor series can extend through several, and in particular through all cabin zones. It is, however, also possible for the temperature sensor system to include several sensor series which extend, at least partially, through different cabin zones.

In the following, the invention is described in greater detail with reference to the attached schematic drawings.

Figure 1 shows a passenger aircraft with components for the temperature- regulated supply of air to an aircraft cabin in accordance with an example of the invention and Figure 2 schematically shows a cross-sectional view of the cabin.

Fig. 1 10 identifies a passenger aircraft, the cabin of which is sub-divided into several cabin zones following on from one another along the length of the aircraft 10. The cabin is here shown as the interior of the aircraft 10 in which the passengers and the

flight crew are located. In the example illustrated, the cabin of the aircraft 10 is sub- divided into six zones, the position and extent of which are identified in figure 1 by arrows. These zones are not zones which are separated from one another into sections. Rather the term cabin zone signifies an area of the cabin which has its own temperature regulation circuit for the regulation of the temperature of feed air which is injected into the cabin zone in question. The cabin zones can therefore also be identified as temperature regulation zones.

Each cabin zone has assigned to it a main supply line 12 by means of which the cabin zone in question is supplied with feed air. In the example shown by figure 1, six main supply lines 12 are provided to correspond to the number of cabin zones.

The main supply lines are connected to a mixing chamber 14 from which they are supplied with feed air. For each cabin zone, the air conveyed by each main supply line 12 is supplied to the cabin area in question by means of a system of air outlets 16 (figure 2). The arrows in figure 2 schematically show the flow direction of the feed air injected into the cabin area. One can see that the feed air is typically injected into the top section of the cabin identified as 18 in figure 2, for example close to the storage lockers 20 for hand luggage. The feed air flows past the passenger seats 22 and is expelled from the cabin 18 at floor level.

The temperature of the injected feed air determines the ambient temperature in the cabin 18. In order to establish a pleasant ambient atmosphere in the cabin 18, the temperature of the feed air for each cabin zone is regulated in such a way that the ambient temperature in the cabin zone in question has a desirable target value. For this, a temperature sensor system 24 is provided, which makes it possible to take one or several temperature readings for each cabin zone. The temperature readings of the temperature sensor system 24 are processed in an evaluation and control unit 26 which carries out a regulation algorithm for the regulation of the feed air temperature. The evaluation and control unit 26 is provided with appropriate software and/or hardware for this. In accordance with this regulation algorithm, it compares an ambient temperature actual value for each cabin zone with an ambient temperature optimum value stored or defined in the evaluation and control unit 26, and establishes the difference between the two values.

With reference to this difference, the evaluation and control unit 26 determines an optimum value for the temperature of the feed air injected into the cabin zone in question. In so doing, the evaluation and control unit 26 works as a regulator which

obtains the difference between the ambient temperature actual value and the ambient temperature optimum value as a regulatory difference.

The evaluation and control unit 26 then compares the optimum value determined for the feed air temperature with the current value of the feed air temperature injected into the cabin zone in question. This current value is provided by a temperature sensor 28 which measures the temperature of the air in the main supply line 12 of the cabin zone in question. In figure 1 a temperature sensor 28 is only shown with the supply line 12 for cabin zone 1. It is clear that this type of sensor 28 is also assigned to the other supply lines 12.

The evaluation and control unit 26 determines a difference from the optimum value for the feed air temperature and the current value. This difference is converted into positional signals for one or several components by the evaluation and control unit 26, by means of which the temperature of the injected feed air can be influenced.

The evaluation and control unit 26 work once again here as a regulator which establishes the difference between the optimum value for the feed air temperature and the current value as a regulatory difference. Components which effect the injection temperature can be, for example, an electric heater and/or a so-called trim air valve.

In the example shown by fig. 1, the temperature sensor system 24 is in the form of an optic fibre extending along the length of all of the cabin zones which is connected to a laser light source 30 at one end of the fibre. The laser light source 30 stores laser light impulses in the fibre of the fibre optic cable. In response to the laser light impulses, reflexion signals are produced by the optic fibre 24 which are detected by an optical detector 32 at the same fibre end and converted into an electric signal.

The detector 32 sends its output signal to the evaluation and control unit 26.

The temperature dependency of at least one optical feature of the fibre 24 is reflected in a corresponding temperature dependency of the reflexion signal in the spectral range and/or in the time range. Because the fibre is a length-continuous medium, a temperature reading can be taken for any point along the fibre. For this, the evaluation and control unit 26 can cut a time window out of the reflexion signal which corresponds to the point in question, and evaluate this.

In so far as the evaluation and control unit 26 determines several individual readings for different points within the cabin zone in question, it establishes from the individual readings an average value which it uses as the ambient temperature actual value in the connected regulation process. If it only determines one single reading for a cabin zone, it is this single reading which is used as the actual value for ambient temperature.