Falcon Spring 2001

• Falcon 20-5 Pressurization Fluctuations
• Static Discharge
• Duncan Aviation Booklet Assists Customers With TAWS Mandate
• Weather Radar Tilt Management

Falcon 20-5 Pressurization Fluctuations

— Ron Grose/Mark Goertzen

Duncan Aviation technicians have recently seen occurrences of pressurization fluctuations in Falcon 20-5 model aircraft. Flight crews describe these as 200-500 FPM fluctuations during climb and descent and during power lever movements.

Most of these aircraft have STC #ST0095KH installed which modifies the outflow valves by plumbing the chambers of the two valves together through a common line with orifices installed in each valve. Many people do not know this modification has been incorporated since the part numbers for the outflow valves do not change. There is usually a small placard located in the vicinity of the outflow valves which states a modification has been performed.

A common scenario occurs when the valves are sent to vendors for the 4,000 hour functional check required by Chapter 5-20. The small fitting which contains the orifice is removed by the vendor. Since the vendor does not know there is a modification incorporated into these valves because the part number has not changed (14331-1C or -2C), the orifice fitting is removed and the plug listed in the CMM is installed; the valves are returned to the original configuration. When the valves are returned to the operator or service facility, technicians install an AN fitting, not knowing there was an orifice in the original fitting sent out with the valves.

To prevent this problem, Dassault has developed SB 745 which modifies the outflow valves to a part number 14331-17 & -18 configuration per a Kollsman SB. With these part number valves installed, it is clear to everyone the valves have been modified. We strongly suggest to all operators who may have this STC incorporated in their aircraft to have SB 745 installed the next time your outflow valves are removed.

Static Discharge

— Kevin Bornhorst

Check the two-piece radome on your Falcon 900, 900EX or 2000 for signs of static discharge. The discharge will appear as pitting across the top of the nose cone section just behind the radome. The reason for this pitting is the anti-static primer was not applied when the aircraft was painted.

Duncan Aviation Booklet Assists Customers With TAWS Mandate

— Ron Hall

If you have TAWS questions, you’re not alone! Duncan Aviation is compiling a booklet entitled Straight Talk About TAWS that delivers answers about the TAWS mandate. Call for a free copy of Straight Talk About TAWS, or email us at: TAWS@duncanaviation.com

Weather Radar Tilt Management

— Jim Wheaton

Storm season is upon us! The technology of radar is a great tool to avoid damaging weather, but it is important to remember its limitations. Radar registers only “wet” objects such as rain, wet hail and wet snow. This excludes “dry” hail, ice crystals and dry snow which are most common at high altitudes. Recently, Duncan Aviation technicians have repaired several aircraft which were flown into damaging “dry” precipitation which was invisible to properly functioning radar systems and alert pilots.

To minimize this possibility, it is imperative that flight crews train, practice and master the use of their radar’s manual tilt function. Some pilots rely on the auto-tilt feature to track cells, but this feature is designed to compensate for aircraft altitude changes only. Instead, the flight crew should manually adjust tilt as the aircraft moves in relation to the storm cell and focus on the most reflective precipitation which is found in the bottom 2/3 of storm cells. Proper tilt management allows radar to see precipitation at lower altitudes and alert the crew to the potential of damaging precipitation at higher altitudes. According to multiple manufacturers’ technical reps, poor tilt management is the leading cause of radar performance complaints.

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