In 1994 I was a very junior First Officer in the process of completing line training with the now ‘late’ Ansett Australia. To my left sat one of Ansett’s most experienced training Captain’s on the 737 who had been on the type since the earlier -200 model had been introduced. I was to be the pilot flying on the sector, a simple hop from Melbourne to Adelaide with clear skies and fair winds, ideal for a ‘bog rat’ like myself attempting to master my first RPT jet.
Cleared for take off on runway 27 I pressed the TOGA buttons to bring the aircraft to life. The autothrottles promptly advanced, hunted a moment for the correct N1 and then held steady. Through “80 knots”, “V1” and “Rotate”, the 737-300 eased into the sky with a minimum of effort. I called for gear up and seemingly no sooner than the undercarriage had nestled into their respective bays, we heard a ‘thump’. Wonderfully indistinctive, the sound was significant enough to be met with a mutual and instantaneous turn of our heads. This was followed by one of those dreaded flight deck phrases, “What was that?” We continued to be focused on the safe ‘clean up’ of the aeroplane and Mike scanned the dials for any sign of trouble. There only seemed to be one slight ‘anomaly’.
Sitting at the bottom of the engine instrument stack sat a pair of vibration gauges. The right hand guage spoke on behalf of the No. 2 engine and was flickering around a reading of ‘2’ units. Per our checklists, no action was required until a reading of ‘4’ was evident and all other engine indications were normal. We were all aware, and wary, of information provided solely on the basis of vibration gauges. They had been integral in the loss of a 737-400 at Kegworth in England five years earlier when an engine failure had been misidentified and the incorrect engine shut down. The vibration guage only indicates a level of vibration in the fan, or front, section of the engine so as I flew the aircraft, Mike set about further investigation. He delved into the touch screen on the centre console known as the ACARS (Aircraft Communication And Reporting System) to reveal further details of the engine’s operation. Within the ACARS, the various stages of the engine revealed their individual levels of vibration and again, nothing stood out. As reflected by the guage, there was only a very slightly elevated level of vibration on the fan of the No. 2 engine. We discussed the option of returning to Melbourne but there was no justifiable indication to do so.
As we topped out in the climb and rolled over into level flight, the thrust levers retarded to the cruise setting and all evidence of the vibration disappeared. The vibration guage now read zero. With all seemingly back to normal, we reviewed the event and had another look at the ACARS; still nothing of consequence. We spoke to Engineering and they had nothing further to offer. On such a short sector we continued to manage the flight and pay attention to the housekeeping duties as the marker for top of descent steadily rolled down the Nav Display. As we pitched in to descent and idle thrust was set, we scanned the engine instruments again. Nothing. Zilch. Ops normal. I decided to delay my head scratching and concentrate on the descent profile for runway 05 at Adelaide which called for a crossing of the coast at Port Stanvac and, hopefully, a smooth decelerating arc over the water to intercept final approach. At that time, Ansett procedures had a minimum ‘spool up’ height of 800’ AGL. In essence, the most efficient descent saw the Boeing glide with the thrust levers at idle until the final stage of approach when, by 800’, the thrust levers were set for power on approach. On this sector my training was bearing fruit and the descent went very close to plan.
On final, wings level, configured and coming through about 1200’ I ‘clicked out’ the autothrottle and manually eased the thrust levers up to an appropriate N1. At about this time it felt like some one had started taking to the aircraft with a sledge hammer. The No. 2 vibration flicked full circle and seemed to bounce off the stops. In a blink, Mike called “taking over” and began to retard the right hand thrust lever back with some resultant relief. The runway loomed large, too late for checklists and a go-around seemed far from prudent. We entered the flare and Mike smoothly closed the thrust levers. The shudder was gone and we touched down right on the money as the Captain pulled asymmetric reverse, not wanting to risk the starboard engine. Clear of the runway, all indications were again normal, though we taxied to the terminal without raising No.2 above idle, just in case.
We parked at the bay and completed our shutdown checklists. The ground engineer plugged in his headsets with the accompanying eardrum rupturing ‘squawk’. Before we had an opportunity to say a word he opened up with, “You gotta see this.” The comment somewhat heightened our interest. After the passengers had disembarked we followed suit and made our way to the starboard nacelle. There was blood on the lip of the cowl indicating a bird strike, but further in a number of fan blades were badly bent. Three of them through almost 90 degrees so that they were pointing forward instead of running around the inner wall of the cowling. There was further biological evidence of the demise of a feathered being that, fortunately for us, had passed through the fan blades of the high-bypass engine but totally missed the engine’s core. This had been the ‘thump’ we had heard shortly after take off out of Melbourne.
Airframe and engine vibrations on board aircraft can be very difficult to diagnose. Their severity is often a combination of such things as airspeed, airflow angle, power settings, and the like. In the event of such vibration, many checklists call for a change in altitude, attitude and airspeed as a possible remedy. In our case, the approach configuration and body angle provided the correct mix for the vibration to fully manifest. Having said that, seeing the resultant damage also reflects the durability of modern jet engines, in this case the CFM56.
Perhaps one of the most valuable lessons that day lay in the nature of the engine problems. Prior to entering the airline world I had spent much of my time training pilots in engine failures of all descriptions. Single engine practice forced landings, engine failures after take off (EFATO) and asymmetric flight in all phases and corners of the envelope. The 737 conversion continued its engine failure emphasis with V1 cuts, engine fires, turbine seizures, failures in the cruise and so on. Almost exclusively, there was a distinct loss of power with resultant yaw. This was then followed by textbook procedures, resulting in a textbook outcome. The real world does not always throw up the standard scenario. It may be a partial loss of power, totally contradictory engine indications or any combination of conflicting information. Whatever the case, the first priority is to fly the aeroplane. Don’t rush in, take a breath and attempt to gather as much information as possible and then manage the situation. Many critical errors have been made in haste.
Until the final stage of the approach on our short journey from Melbourne to Adelaide, all we effectively experienced was a ‘bump’ and an ‘in tolerance’ vibration indication that subsequently disappeared. To see the fan blades of that starboard engine you would have expected far greater drama. We are all trained for when things go terribly wrong. We have drills, procedures and checklists in place to keep the most injured aeroplane aloft. Unfortunately reality doesn’t always fall within the guidelines of a syllabus. Be it the crippled DC10 at Sioux City or the more subtle confusion of Kegworth, neither were a ‘standard’ training scenario prior to the event. Certainly, on occasions emergencies are easily read and then again, sometimes it’s the little things.
