Lear Romec Fuel Pumps Rock solid simplicity (with a few rough edges)
By Randy Knuteson
Nome, AK. The pilot was about a mile out and on final approach when he first noticed flames blazing from the left engine nacelle of his Piper Navajo. Immediately, as if by instinct, he shut off the flow of fuel to that engine. An uneventful landing was followed by a successful, yet frantic, attempt to extinguish the remaining fire fed by residual fuel.
Two months passed. Sparta, TN, another pilot, another Navajo, another fire. Fortunately, the pilot had noticed excessive fuel consumption and had diverted to the nearest airfield. Upon landing and rollout, he realized the left engine compartment was trailing flames. The plane sustained substantial damage. The pilot was unscathed; his preemptive action possibly saved his life and the lives of his five passengers.
In both cases, investigators' attentions were drawn to the engine-driven fuel pump. Closer scrutiny revealed that fuel had sprayed from the parting surfaces where the relief valve housing mates to the pump body, bathing the rear section of the engine compartment with 100LL. Lycoming closely examined new pumps back at the factory. An analysis of seven similar pumps revealed that four of the seven also leaked in the same gasket area.
Chronology of a crisis
Were these isolated incidences? A perusal of applicable Service Bulletins would lead you to believe otherwise. As far back as 1976, Lycoming had issued a Service Bulletin (#406) addressing the importance of inspecting Titan and Lear Romec fuel pumps for potential leaks caused by insufficient tightening of the cover screws. It was further discovered that these cover screws could possibly loosen due to the gasket material either taking a set or shrinking with time.
Lear Romec attempted to redress this problem by substituting a rubber material for their asbestos/paper-based gasket. The goal was two-fold; to choose a material that would not be as susceptible to shrinkage while eliminating the perceived risks associated with an asbestos type gasket. Unfortunately, what appeared to be a workable solution only turned out to worsen an already bad situation. The rubber gaskets also took a set, and seeped fuel. Furthermore, these rubber gaskets suffered from their tendency to deform and extrude out from the parting surfaces when re-torqued, occasionally spraying fuel across hot exhaust surfaces.
Continued field reports of leakage prompted the manufacturer to release Service Bulletins 101SB012 in 1985, bulletins 101SB017 and 101SB018 in 1987, culminating with 101SB020 in 1997. All the aforementioned bulletins dealt with re-torquing the relief valve housing screws at scheduled intervals in an attempt to prevent the onset of any fuel seepage. Textron Lycoming issued Mandatory SB 529 in December of 1997. Airworthiness Directive 98-18-12 (a reprinting of SB 529), mandating these repetitive torque checks, was implemented the following year.
The process of inspecting relief valve cover screws and pumps for fuel leaks at 50-hour intervals brought an interesting anomaly to light. Mechanics soon discovered that fuel pumps having the composite gasket manufactured by Consolidated Fuel Systems (CFS) consistently required no further tightening. Many became tired of wrestling with pumps buried deep within the engine and were anxious for some form of relief.
Solution? A modified pump
More recently, Crane has opted to redesign the entire valve housing of their Romec pump in an attempt to eliminate the troublesome gasket. Their new design incorporates packing type seals commonly seen in industrial type hydraulic pumps. Recesses machined into the relief valve housing serve to capture the seals internally. This third attempt to address the ongoing issue of fuel leakage appears to have solved the problem. Modifying these pumps eliminates the need for repetitive torque inspections. Modification kits for the Romec Pumps may be purchased from Crane Manufacturing (see Lycoming SB 539). The cost of these kits range from $285-315 depending upon which model of pump you are modifying. Crane has replaced the gasket with a ladder-shaped packing and also designed a circular packing for the opposite side of the housing where the diaphragm is positioned. Pumps are to be converted by authorized repair stations.