Michael J. Mercer

A likely reason for the cracking problem is the higher CHTs experienced by these cylinders. The cylinders ARE NOT direct replacements for TCM cylinders because of their increased volumetric efficiency. Unfortunately the FAA has allowed direct replacement but not also mandated a corresponding increase in the full power fuel flows to compensate for the increased volumetric efficiency (i.e more air without more fuel). The result is an effective leaning of the full power mixtures with corresponding increases in the CHTs at full power. This extra heat, predominantly for aircraft that spend a higher proportion of their time at high manifold pressures, accumulate the most time in this insufficiently rich operating condition. This is exactly the observed failure behavior noted in this NPRM. I had attempted to address the issue directly with the Federal Aviation Administration MIDO in Ft Worth, Texas. Apparently that FAA office provided the approval for the Superior cylinders to be direct replacements for the TCM cylinders. In my conversations with that office in 2005, Jurgen Priester was totally unwilling to look into the matter and, of course, Superior was equally uncooperative is presenting any infomation regarding the long term impact of running full power with an effectively leaner mixture. I guess we know the result now three years later. I hope nobody died as a result of this FAA inaction. The corrective action should be an immediate authorization to increase the full power fuel flows above the type certificate limits as necessary to return the fuel-air ratios to those of stock TCM engines. That way we can all spend less time looking for problems after the fact and start avoiding the problems in the first place. I'd also note that ECI cylinders will experience this problem although not quite as significantly as for the Superior cylinders. The ECI cylinders also have higher volumetric efficiencies then TCM cylinders but not quite as high as Superior. If higher volumetric efficiency cylinders are allowed on these engines without also mandating a full power fuel flow increase, the cylinders will run hot, with obvious long-term impacts.