Boeing 787 Ice and Rain Protection

The Boeing 787 protects itself against ice in three ways. Electro-thermal heating blankets in the wing slats replace the hot-air wing anti-ice of earlier jets, the engine cowls are still anti-iced with air from the engines, and the flight deck windows and air data probes are heated electrically. A primary ice detection system switches the wing ice protection on by itself, and wipers clear rain from the forward windows.

The design reasons, from power consumption to drag, are explained in Boeing 787 no-bleed systems architecture; this article covers how the systems are built, what the crew sees and what the MMEL requires when parts fail. It draws on the FAA Master Minimum Equipment List (MMEL), the FAA Flight Standardization Board (FSB) reports, Boeing's 2007 AERO article, written before entry into service, Boeing's airport planning document and the type-certificate data sheets. The A220's systems are described in A220 ice and rain protection.

Ice detection

The 787 has a primary ice detection system (PIDS), operable in flight in all day and night lighting conditions, which detects icing conditions and automatically activates the wing ice protection system. The MMEL lists two ice detectors. One may be inoperative for dispatch, and both may be if alternate procedures are established and used.

The crew can also see the wing. Wing lights mounted on the fuselage illuminate the wing leading edge, and analysis showed that they cause no glare or reflections that would handicap the crew.

Electro-thermal wing ice protection

The wing is protected by the wing ice protection system (WIPS): several heating blankets bonded to the inside of the protected slat leading edges. Energised all together, they anti-ice; energised in sequence, they de-ice. In Boeing's pre-service description the system needs about half the power of a pneumatic system, because no excess energy is exhausted, and with no bleed air exhaust holes it reduces drag and community noise. The original FSB differences table simply lists wing anti-ice as electric heater blankets.

The MMEL describes 48 heat zones, mirrored on the left and right slats, and three wing ice protection channels, two of which are required for dispatch; one heat zone pair in symmetrical slats may be inoperative. Two wing anti-ice (WAI) indications are listed. With the whole WIPS inoperative, the aircraft may be dispatched only if it is not operated in known or forecast icing conditions and the flight remains within 120 minutes of a suitable airport. For crews coming from the 777-300ER, the FSB lists the ice and rain protection controls and indicators, the windshield washer and wing anti-ice as design differences, all at level A, self-instruction.

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Engine anti-ice

The engine cowls are the one place where the 787 still uses engine air against ice. The original FSB report lists pneumatic ice protection for the engines, and Boeing's airport planning document calls the remaining pneumatic system engine nacelle anti-ice. Each engine anti-ice (EAI) system has a pressure regulating and shutoff valve (PRSOV), a pressure regulating valve (PRV) and two pressure sensors, and the MMEL lists two EAI indications. The current FSB report describes the pneumatic chapter as engine anti-ice only and rates its differences from the 777-300ER at level A.

The engine data sheets confirm the arrangement. Every Rolls-Royce Trent 1000 supplies compressor air to the airframe only for nacelle anti-icing, the anti-icing flow demand being modulated by a regulating valve; only the Trent 7000 models covered by the same data sheet supply cabin bleed. For the GEnx-1B, the aircraft data sheet records an equivalent safety finding titled "GEnx Cowl TAI Duct" for the 787-8 and 787-9, TAI standing for thermal anti-ice.

With one EAI system inoperative, dispatch needs its PRSOV locked closed, the associated engine ignition systems working, its engine anti-ice switch OFF, no flight in known or forecast icing and a 120-minute limit. On Trent-powered aircraft, and on GEnx aircraft with a later change incorporated, a failed PRSOV may instead be locked in a mid position, provided its PRV works, operations are limited to an OAT of 38 °C or below and performance adjustments are applied. The duct leak overheat detection system is tied to engine anti-ice too: with one of its two systems inoperative, the associated engine anti-ice switch must stay OFF (Boeing 787 APU and fire protection).

Cabin air compressor inlets

Because the 787 takes its cabin air through dedicated inlets to electric compressors rather than from the engines, those inlets need ice protection of their own: the MMEL lists two cabin air compressor inlet ice protection systems (CIPS). Whenever one or both are inoperative, the airport OAT must have stayed at or above -35 °C since the last landing. With both inoperative, both packs must also work and repairs are due within 30 calendar days; with one inoperative, either the opposite pack must work or the aircraft must avoid known or forecast icing and stay within 120 minutes of a suitable airport. The compressors themselves are described in Boeing 787 air conditioning, pressurisation and oxygen.

The EASA certification basis of the 787-8 and 787-9 also includes a special condition on engine and APU intake icing in falling and blowing snow.

Probe and window heating

The air data probes and the flight deck windows are heated electrically. The air data system relies on three heated pitot probes, left, centre and right, and failure of one or more pitot probe heat systems produces a caution-level EICAS alert. The MMEL treats the centre probe more strictly than the side ones. With the left or right heater inoperative, the other two probes must be inspected before each departure, their heaters and air data modules must work, and approach minima must not require the inoperative system. With the centre heater inoperative, the aircraft must also stay out of visible moisture and known or forecast icing, and within 120 minutes of a suitable airport. On aircraft with a later change, the MMEL also lists a total air temperature (TAT) probe heater system.

The flight deck windows have heat channels of three kinds:

One forward primary channel may be inoperative if its switch stays off, the associated backup channel and the side window channels work, the aircraft avoids known or forecast icing and the flight stays within 120 minutes of a suitable airport. The window heat switches carry INOP and ON lights, and the window heat software is listed as three items, two of them required for dispatch. The principles are in probe heat, window heat and rain protection.

Rain removal

Each pilot's front window has a windshield wiper, with low speed, high speed and intermittent functions. The wiper panel is in the same location as on the 777 but now carries washer switches for the windshield washer system, which the FSB lists as a difference from the 777-300ER.

With the wiper system inoperative, the MMEL allows dispatch only if the aircraft is not operated in precipitation within 5 statute miles of the airport of departure or intended landing and approach minima do not require the wipers. A wiper may lose its high-speed function if its low speed works, and the reverse.

Operating in icing conditions

The EASA data sheet approves the 787 for flight in icing conditions, and the original FSB report states that its ice protection provisions meet the requirements that allow the operations defined in 14 CFR 91.527, operating in icing conditions. Automation helps the crew: the primary ice detection system turns the wing ice protection on when it detects icing conditions, and the fuselage-mounted wing lights let the crew check the leading edges at night. The same list of approved operations includes wet and contaminated runways, where the antiskid described in Boeing 787 landing gear and electric brakes does its work; the full list is in Boeing 787 family and flight deck.

The MMEL's dispatch conditions show which parts of the system the 787 relies on in ice:

Ground de-icing and the general theory are covered in aircraft ground de-icing and anti-icing, airframe icing and ice protection and ice detection.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.