Date: 201305
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Dash 8-400
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion
Second reporter function: First Officer; Pilot Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Weight And Balance
Detector: Person Flight Crew
When detected: Pre-flight

Narrative: Upon receiving the CLR after departure time; my FO put the info into ACARS Weight and Balance and received confirmation that we were ok for departure; associated weights; and V speeds. After departure we reviewed the data; caused by a discussion about how bag heavy we were; and determined that we had exceeded the Aft Cargo Load Limitation by 14 lbs. (Cargo limit was 2545 lbs and we had 2559 lbs) Upon arrival Maintenance Control and I determined that because no major weight [had changed]; i.e. MTW; MZFW or MLW; there was no inspection required and therefore no write up required; as this is was a minor exceedance and our whole Weight and Balance system is based on averages. My concern is: We also sent an incorrect amount of bags the first time that should have returned a 314 lb error and it also didn't. We noticed that error quickly and changed the numbers and re-sent the transmission and should have gotten an error of 14 lbs and didn't on either. Also; that a crew may inadvertently takeoff way over weight if the system information is not working properly; and the way we are trained. It should work.  Find out why ACARS 'glitches' and did not; as it has every other time; given us an error with an associated solution...i.e. Aft cargo exceeded by X amount; or move X amount from aft to forward.


Second narrative: I accidentally entered incorrect bag data which would have overloaded the aft cargo by over 300 lbs. ACARS kicked back a solution with no errors; even though I told it the aft cargo had 314 lbs too much. I noticed my mistake; [and] then reentered the CLR info into ACARS correctly. It kicked back a solution with no errors; so we proceeded on and took off. After taking off; I did the math on my own. The limitation for the aft cargo is 2545 lbs total; with max 1000 lbs on the aft shelf. That works out to be 84 bags total; of which 33 bags max on the aft shelf. ACARS also allows a cargo weight input on top of the bag count.  After all was said and done; our actual aft shelf cargo weight was 14 lbs over weight limitations. Both ACARS solutions that I sent to [system] kicked back solutions that allowed the exceeded limitation. Normally; [the system] will send you a remark telling you what the error is and will not give you any numbers; but on this specific aircraft; it did not. After landing we contacted Maintenance and they told us that since no major limitations were exceeded (i.e. MTOW; Max Zero Fuel Weight; MLW; etc.); there was no inspection required. We need to verify the system database for this aircraft and find out why it did not give us an error. In the cockpit; ACARS is our primary source for Weigh and Balance information and we shouldn't have to second guess it.


Synopsis: The crew of a DHC-8-400 sent erroneous information through ACARS and received takeoff data in reply; then discovered after takeoff that the weight and balance system not only failed to detect and indicate the incorrect input; but also did not discover and indicate the obvious weight discrepancy.