Global Supply Systems

Comments on NPRM We operate three B744F aircraft with GE 80C2 engines with Primary Ice Detection System/Auto NAI and Autostart/Autorelight facility. Our area of operation includes a high proportion of flights in regions that have been particularly affected by ice crystal accretion incidents and are therefore concerned as to the risks associated with this current problem. However we consider that for aircraft with our equipment level, the proposed procedures requiring selection of manual Anti-ice during descent in visible moisture to be too prescriptive for the following reasons; 1. The procedure is required irrespective of altitude, so that nacelle anti- ice will frequently be required to be selected ON unnecessarily particularly at lower altitudes where ice crystal ingestion and subsequent flameout has not been experienced. 2. Our crews have become accustomed to the use of automatic ice detection and are hence less familiar with the detection of conditions requiring the manual selection of Nacelle Anti-ice. There will be an increase in workload during descent as the external ambient conditions are assessed more frequently for the requirement to select NAI. This is particularly relevant at lower altitudes where ATC and Approach procedures generate a higher workload than during the initial descent 3. The increase in idle thrust level incumbent on engine anti-icing increases the descent distance required. The use of FMC descent predictions is essential for environmental and economic reasons to minimise fuel. Descent is basically predicated on non use of NAI, and hence any required selection of NAI negates this prediction. The FMC can be programmed to take account of the effect of NAI below an entered altitude but this is a very blunt tool. The net result of the proposed procedure is that either the aircraft becomes high and fast due to leaving inadequate distance for descent, with a decrease in approach stability, of conversely, descending too early, with increase in fuel usage and noise disturbance for level type flight at low altitudes. 4. We understand and support measures to reduce the risk associated with ice crystal accretion but believe that forcing use of Manual NAI particularly at lower altitudes is deleterious to safety, rather than enhancing it. 5. The proposed procedures are all procedure related. GE have two software revisions to the EEC bleed scheduling which whilst not preventing the problem occurring, do appear to mitigate the effect. The later one is subject to a current AD 2007-12-07 requiring compliance by 10 Jul 2012. Upgrades are only required on workshop visit for unserviceability or engine change. With current serviceability levels the mandatory upgrading of current equipment is extremely slow, leading to substantial levels of unmodified software installed on aircraft. Whilst this increases pressure to introduce procedural alleviation, it does not adequately address the improvement in safety that would be incumbent on bringing the compliance date forward, requiring use of a programmed upgrade of the EEC software. 6. We understand that a similar process requiring use of Manual activation of NAI of a different type/engine combination which also suffers from ice crystal ingestion problems, allows reversion to Auto NAI below FL100. We therefore request that serious consideration be given to; 1. Removing the requirement to select Manual NAI in visible moisture below a TAT of 10C during descent at lower altitudes e.g. below FL100 2. Revising the current AD 2007-12-07 to require a much earlier compliance date.