EMB ERJ 145 ER/LR
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; General Declared Emergency
Aircraft
After takeoff the position of the landing gear was uncertain.  Declared an emergency.   Ran checklist per EMB AOM Volume One. Returned and landed safely. A malfunction of the LGEU. More checks of the LGEU.
Upon selecting gear up following a normal takeoff; I observed an immediate shift from gear down to gear up on the EICAS display. The transition occurred in less than 1/2 second; and no 'in transit' indication was shown. The indication on all 3 landing gear indicators was perfectly synchronized and inconsistent with normal landing gear retraction. Slightly after this time; the wind noise in the cockpit diminished somewhat (consistent with nose wheel retraction and door closure). Based upon the timing; noise; and unusual EICAS indication; I advised the pilot flying that we were experiencing a probable landing gear malfunction. The Captain then displayed the second page of engine information on the #2 RMU; which indicated the landing gear to be 'down and locked' while the EICAS showed the gear position to be up. At this point; my assessment of a landing gear problem was confirmed; and with the concurrence of the Captain; I declared an emergency with the Departure Controller. Upon running the 'LG Lever Disagree' checklist and selecting gear down; the EICAS display again immediately displayed 3 green 'gear down' indications in less than 1/2 second and with no 'in transit' indication. Wind noise in the cockpit increased consistent to the nose gear doors opening; but my 'gut feeling' told me that no landing gear movement had occurred. Upon retracting the landing gear per the checklist; the same behavior was noted as during the initial takeoff gear retraction. Once again the EICAS showed gear up; while the RMU #2 showed gear down and locked. We transitioned to the Abnormal Landing Gear Extension Procedure; and observed the same behavior as previously stated when selecting landing gear down. EICAS and RMU displays showed gear down and locked. I knew this to be a faulty indication. This time; I selected the 'Doors' position on the Gear Electrical Override and noted no change in wind noise (nose gear doors were already open). I waited 3 seconds and selected the 'Gear/Doors' position on the Gear Electrical Override and noted a distinct aircraft shudder; 3 distinct 'thumps' (consistent with hydraulic movement and gear reaching the down position); and a slightly elevated wind noise. I now suspected the landing gear to be down and locked. We performed a precautionary overflight and the Tower confirmed that our landing gear appeared to be down and locked. No further inputs were made to the landing gear lever or override switch (I did not want to attempt retraction). I conferred with Maintenance and Maintenance Operational Control (MOC) on the radio and determined this to be our safest aircraft configuration for landing. We then returned for a normal landing. As a further indication of irregular landing gear operation; I had to manually select T/O-1 thrust rating during the before landing checklist (which normally occurs automatically with gear down selection). An uneventful (and very smooth) landing was performed by the Captain; and after the aircraft was stopped; we had Maintenance install the gear pins and tow the aircraft to the gate for passenger deplaning. At no point during the flight was a single relevant EICAS Warning; Caution; or Advisory message displayed. This is a fact which I find particularly concerning.Aircraft landing gear malfunction and faulty landing gear indication on the EICAS and RMU displays. An astute and well-trained crew identified; diagnosed; and corrected the problem with the luxuries of good weather; ample fuel; and adequate ground and ATC support.The EICAS landing gear position indication system did not perform its stated function of reflecting the true landing gear position. Further; the RMU #2 landing gear indication stayed on 'gear down and locked' which was also a faulty indication for the majority of the flight. Not a single caution or warning indicated the disagreement between these two systems; though one existed several times during the flight. Quite simply: the EICAS gear indication and RMU gearindication need to be cross-checked automatically and an error message generated on the EICAS in the event of a disagreement. Additionally: the complete retraction or extension of all landing gear in less than half a second (without any 'In- Transit' time) could be used as a secondary indicator that a landing gear problem may exist. In short -- only the intuition of a well-trained crew prevented a gear-up landing with 3-green lights on the EICAS.
EMB 145 landing gear did not retract when selected up; an emergency declared and an uneventful overweight landing accomplished.