Equipamientos y recursos para la Interpretación

Probably the most efficient way to perform remote ice detection will be the use of an integrated system of airborne radar, ground radar and satellite data.

At present remote detection is very expensive and technologies are not mature yet for a commercial application. A lot of research however is going on in this area.

5.7) Detection beyond Appendix C

No aircraft has been tested to fly safely in conditions beyond Appendix C (Mean droplet diameter larger than 50 microns). Therefore it is fundamental for the pilots to identify and avoid these conditions. To help the pilot in recognizing such extreme conditions a number of visual cues have been identified:

• Unusually extensive ice accreted on the airframe in areas which usually do not collect ice (i.e. side window on ATR).

• Accumulation of ice on the upper surface of the wing aft of the protected area. • Accumulation of ice on the lower surface of the wing aft of the protected area. • Accumulation of ice on the propeller spinner farther aft than normally observed. • Accumulation of ice on engine nacelle farther aft than normally observed.

In addition to these cues, signs which could indicate the presence of SLD are the following: • Water splashing on windscreen at negative outside temperature.

• Visible rain at negative outside temperature.

If one of these cues is seen by the crew, the evasive procedure, as defined within the Aircraft Flight Manual, must be applied.

5.8) Ground ice detection

5.8.1) Before de/anti-icing procedures

The first concern for the crew is to determine whether the de/anti-icing procedures need to be applied for a safe take-off.

In order to supplement all the available visual cues such as refractive plates and tufts (fig. 5.3), various ice accretion sensors have been developed. Pinpoint (spot) sensors may be adequate to monitor limited critical areas with homogeneous ice formation (i.e. to address over the wing icing after cold soak), but they cannot identify the conditions of the whole lifting surfaces whatever the number of sensors might be.

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Even if a sensor shows a good reliability to detect any contamination (frost, snow, ice, as single or combined layers) it will not ensure that the aircraft surface in its immediate vicinity has the same ice contamination level. Although a tactile inspection, when possible, is always the best way to clear up any doubt, research is under way and the following systems are showing some promising results.

• BFGoodrich : HALO system. The wing skin is used to guide ultrasonic waves which are generated and received by transducers mounted beneath the surface. The system is able to detect and discriminate several contaminants according to the skin response. Several sensors (transducer/receiver) installed in a grid could cover and monitor the whole critical surface. On the other hand, aThe high number of components may be detrimental to the system reliability, moreover it has to be checked if the sensor response is not affected by wing load variations.

• Aerodynamic performance monitor. Licensed to BFGoodrich, this very powerful system is able to detect any over wing contamination, provided it has been carefully calibrated on a clean airfoil. One sensor installed at the wing trailing edge can monitor up to 1m spanwise at the leading edge.

The system requires a minimum airflow in order to satisfactorily operate and it can only be used during the initial take-off phase. If a detrimental degradation is found during the initial take-off run, a warning must be produced well before V1. A high number of sensors are still required to cover the full span of the lifting surfaces.

• ID-1 from RVSI. Ground based or aircraft mounted cameras associated with specific software for imaging treatment, allow for the detection of ice formation or snow deposits over the aircraft surfaces. The information is provided to the crew or the ground personnel through a screen.

The reliability of the system still needs to be investigated for all skin materials. Again several cameras need to be installed on aircraft to monitor the various lifting surfaces.

5.8.2) After de/anti-icing procedures

When the duration of protection (after a de or anti-icing fluid application),indicated by special tables called Holdover Time Tables (annex 2), has elapsed or when the crew are in doubt about the intensity of precipitation a visual inspection will be carried out by the crew or qualified ground personnel. If a fluid failure (appearance of ice formation or loss of gloss) is detected or if the crew have any doubt about it, the aircraft shall receive a new de/anti-icing treatment. An

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• To help the crew take a decision and enhance safety.

• Not to perform a supplementary de/anti-icing procedure when unnecessary and then not to delay the take-off any further.

• To decrease fluid waste and runway contamination (poor friction coefficient). • For the ecological impact.

In addition to the detection technologies described above, some equipment manufacturers have developed means to monitor the fluid de-icing capability. The sensors are punctual and flush mounted to the surface.

• Techniques based on a Peltier device. The freezing temperature of fluid/water mixture is dependant upon the water ratio (the greater the amount of water the higher the freezing temperature). The surface of the sensor (vibrating membrane) is cooled with a Peltier device (cooled when electrically supplied) to get an ice signal. The freezing temperature is then compared to the ambient temperature. When the freezing temperature of the mixture is too close or above the ambient temperature, a warning signal is produced. • Techniques based on ultrasonic waves. The fluid/water mixture provides different

signature to an ultrasonic wave according to the water dilution. For a given fluid, according to the ambient temperature, it is possible to predict for which dilution it will freeze. A warning signal will be produced when, according to the external temperature, the mixture is too close to freezing.

All these technologies are still under development and are far from a certification status as a primary device. It is also important to remark that, because of different fluid flow-off characteristics, according to the type of fluid, the loss of effectiveness may occur at different location of the wing. This, in addition to the fact that fluid coverage is rarely homogeneous, implies that the actual location in which the detectors are installed greately affect the system effectiveness.

5.9) Other indicators

The detection principles listed above are not comprehensive. Any other means, provided they have been validated, can be used by the crew. The following are known to be used :

• Wing aerodynamic buffet. • Vibrations on control stick.

• Ice accretions on wing leading edge. • Performances reduction.

• Noise due to ice shedding. This is mainly valid for ice accumulating on propellers. Ice naturally sheds from the rotating blades due to centrifugal forces. So, as soon as ice is shed from the blades, ice slabs may impact the fuselage so announcing the presence of icing conditions. It could also be a clear evidence of the icing conditions or an indicator of the propeller ice protection system. If the outside temperature is very low or if the propeller de-icing is inactive (switched off or failed), the ice slabs will be larger (increase of the ice adhesion force) and a louder noise will be produced.

• Propeller imbalancing due to ice.

5.10) Cockpit indications

There are several methods to inform pilots about icing conditions. The most used method in a non- Cathode Ray Tube (CRT) type of cockpit is a ‘Master Caution Light’ in conjunction with other

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warning lights. This method is often used where ice protection system controls must be manually actuated. Other systems which automatically energize ice protection systems, merely report the presence of ice via a panel light or in some cases not at all. In a CRT type of cockpit a phrase such as ENGINE ICING or AIRPLANE ICING is used to alert the crew of an icing encounter. A fail signal is available on some ice detector units.

5.11) Ice detection summary

Method Typical Technology Classification Status

Differential Pressure Detection

Pressure Array Detectors Detection of icing conditions

Progressively abandoned

Obstruction Ice Detection

Light beam interruption; Beta beam interruption;

Rotating disk Detection of icing conditions Progressively abandoned Vibrating Probe/surface Ice Detection Piezoelectric; Magnetostrictive; Inductive Detection of ice condition, ice thickness and ice

accretion rate

The most used technology

Latent Heat Ice Detection

Periodic current pulse; Power Measurement Detection of icing conditions Progressively abandoned Microwave Ice Detection

Resonant surface waveguide (dielectric) Detection of icing conditions In development Electromagnetic Ice Detection

EM source (visible light,

infrared, laser, nuclear beam) Visualization of surface

In development

Pulse Echo Ice Detection

Piezoelectric transducers Detection of ice condition, ice thickness and ice

accretion rate

In development

Remote sensing On board radar, ground radar, satellite

Detection of icing condition in front of

the aircraft to avoid inadvertent icing

encounter

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