B737-800
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 131; Flight Crew Type 11000
Confusion
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
General Maintenance Action; General Declared Emergency
Aircraft
Time of first incident was when the aircraft attained an IAS of 90 knots in HGS (after the 80-knot callout.) The nose wheel began to shimmy. As airspeed increased while still on the runway; the shimmy began to intensify. Liftoff was otherwise normal except while the nose gear was retracting; an unstable swiveling oscillation of the nose wheel created vibrations that were heard and felt throughout the entire aircraft; until about a minute after gear retraction into its up-locks. Then my First Officer and I began to smell an unusual odor. At first it smelled like melted cooking butter; but then the odor changed to some kind of burnt food; to finally an odor of burnt rubber. At no time was there ingress of smoke or caustic fumes to the flightdeck or cabin. To confirm this I turned on the cockpit dome light (since it was night time.) A look of all engine parameters showed normal. I asked my First Officer (pilot not flying) to pull out his O2 Mask and don it; and called for the QRH Smoke/Fire/Fumes; and Aircraft Smoke/Fumes Removal Checklists while I placed both air conditioning packs to high flow (to remove the odor). Both the 'A' and 'B' Flight Attendants were on the intercom telling me they were discussing the smell and that passengers were also concerned. Flight attendants described the odor as burnt butter at first; or food; later more as burnt rubber; but when asked they agreed it was just a smell; it was NOT electrical in nature; and not caustic; and that they did not observe any smoke. I concurred. I told my flight attendants I would make a PA to alleviate the passengers' concerns. Meanwhile; my First Officer was referencing the QRH and; at that time; the packs in high flow caused the smell to completely dissipate (but we continued to monitor all systems; and continued to be vigilant.) I considered the QRH checklists complete. As an additional resource; I contacted my Dispatcher; and asked him; 'Will you ask Maintenance Control is there any history on this aircraft; including any history of any of our fleet having experienced the smell of burnt rubber after a shimmying nose wheel retraction?' My Dispatcher replied that Maintenance stated we may have blown a nose wheel tire; but otherwise; there was no relevant history to pass on. By this time we were far out of radio range of Tower to find out if there were any remnants of rubber on the runway. At this point; it was agreed no safer course of action than to continue on was warranted; and Dispatch suggested having the fire trucks standing by on landing. Based on the realization from Maintenance that we may have a nose wheel tire blown; consideration was made for a possible evacuation; although minimal; but not impossible. So I briefed the flight attendants to prepare the cabin; but I added I believed it was highly unlikely; and was only a precaution. I made a second PA informing the passengers with a brief description; and saying...as a precaution we have asked the Tower to have the airport fire department on standby; so don't be alarmed by the presence of the fire trucks. We completely expect this to be a normal landing ... erring on the side of caution ... the flight attendants will be yelling out their commands; as they are trained to do; so please follow their instructions; and please don't be alarmed. At this point; the impact from continuing the flight was mitigated by absence of smoke; fire; or fumes. The new incident was that of the integrity of the nose wheel on landing. Landing runway distance was more than adequate. I briefed my flight attendants to review their tasks; and what our intensions were. My First Officer and I reviewed our QRH evacuation procedures and what our intentions were to each other. Stipulated we could not perform a go-around once on the ground due to possible FOD of nose wheel tire(s) debris ingesting into engine(s). Upon lowering the landing gear; I observed three green landing gear down indications; and informed the Tower. We asked Tower what frequency the fire rescue was monitoring; and he stated; you may switch to them now. Then my First Officer informed fire/rescue of our intended touchdown point; and that it was our intention to stop on the runway for nose gear inspection. A normal main gear landing was made (without autobrakes; so as to avoid a heavy load on the nose gear by deceleration forces); but when the nose wheel touched down; we immediately felt the same vibration and shimmying effect of the nose wheel on rollout; as we did on takeoff. Braking was smooth and gradual. We came to a complete normal stop easily. I set the parking brake; turned off my landing lights (since fire/rescue were approaching the aircraft from the front); but kept all other lights on; until they inspected the nose gear and gave the all clear. Once the fire/rescue departed; we continued to our gate and shut down. A logbook write-up was made; with close consultation with my Dispatcher; Maintenance Control; the Chief Pilot on Call; Contract Maintenance; [and] then Crew Scheduling for duty time and an engine run at the gate.On post-flight inspection of the nose wheel bay; it was noted that the spin-down pads (snubbers) had an inordinate amount of rubber; a lot more than usual according to contract Maintenance. Additionally; there were splattering of rubber matter throughout the ceiling of the gear bay. The strut appeared to be over inflated in my judgment. I also suspected that tire pressure was higher than usual; which would account for the rubbing of the hot shimmying tire upon gear retraction; which in my estimation was the cause of the rubber being super-heated; which caused parts of the tread of the tire to melt; and then be thrown about in the gear bay area. It (bits of rubber) had to be in a melted state; because it stuck to the surrounding area; where it cooled and stayed intact. It could not have been in anything other than a melted state; because of the way it stuck to the ceiling of the gear bay. Prior flight crew must have experienced the nose wheel shimmy on their landing; but when the aircraft was handed off to us; their comment was 'it's a good airplane.' We were completely taken by surprise when the nose wheel shimmy occurred to that degree of intensity having not occurred on the prior landing.
Shortly after reaching 80 KTS; the nose wheel began to shimmy. As aircraft airspeed increased; the shimmy intensified. The takeoff was continued since at no time did we believe that the aircraft was unsafe to fly. Rotation was normal and Pilot Flying (Captain) called for landing gear up. Positive rate was confirmed and landing gear was selected to up. When gear retracted into the wheel wells; the nose wheel spinning against the snubbers created a pronounced amount of oscillation and vibration before the nose wheel came to a stop. At this point we were climbing out; being handed off to Departure; retracting the flaps per SOP; and flying out on profile. After climbing through 10;000 FT; we began to discuss the situation in more detail as to what caused the smell and vibration. We both came to the conclusion that the nose wheel was most likely the issue. The Captain decided to confer with Dispatch and Maintenance to use all resources available and make sure we had all the information possible. We were still proceeding to destination since there were no other problems. The Captains' communication with Dispatch took some time; but finally; they suggested that one of the nose wheel tires could have blown. While this had not seemed likely to us; we then thought it could have been a possibility. At this point we were well on our way and; between Dispatch; Maintenance and the Captain; it was decided that the best course of action was to have the fire trucks ready in case we had a problem with the nose wheel. While we did not believe there would be a problem; we thought it would be best to err on the side of safety and have the trucks ready. With the weather being good and the availability of a long runway; we calculated our landing data (flaps 40 for slowest possible speed at touchdown) and determined it was acceptable. Descent; approach; and arrival were uneventful. An emergency was declared. We were given landing clearance and also allowed to communicate directly to the fire trucks. We coordinated with Tower and the trucks that we would bring the aircraft to a stop on the runway and have the trucks access the nose wheel. A soft landing was made and the nose wheel was lowered gently. Upon contact of the nose wheel to the runway; there was noticeable shimmy and vibration. Aircraft was brought to a stop and we told Tower and the trucks that the aircraft was stopped and the parking brake was set. The fire trucks approached the aircraft and firemen inspected the nose wheel and gave us the all clear.
B737-800 flight crew reports a strong nose wheel shimmy above 90 KTS during takeoff and continues. The vibration continues after gear retraction and eventually a burnt rubber odor is detected. Flight continues to destination where an emergency is declared and a normal landing ensues; with nose wheel shimmy again detected when it touches the runway.