Date: 201809
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Aircraft component: Engine Air Anti-Ice
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown; Troubleshooting
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural MEL / CDL; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem
Contributing factors: Procedure; MEL; Aircraft; Company Policy
Primary problem: Ambiguous

Narrative: Flight was delayed due to a late inbound aircraft. When we arrived at the airport I called Dispatch for a brief and to discuss the proposed departure time. In the brief we discussed the MEL that was applied to the aircraft for the anti ice valves. The valve in question was wired to the open position and the MEL stated several things:MEL #30-XX-XX-X: TO (takeoff); Engine override knob placed in the engine position for the entire flight/all phases. Engine ice on applied to the TLR (Takeoff Landing Report); Weight penalty applied; these stipulations were discussed in the brief.Once I received my paperwork I reviewed the TLR and saw that the penalties had been applied in the [takeoff] section. However I missed that they were not applied to the landing section.On the arrival the First Officer stated that the ACARS wasn't giving speeds because of a note saying that engine A/I not required with temps above 10C. I then said then we would have to utilize the TLR to get our required numbers. This is where I noticed the lack of engine A/I on for the landing performance. I sent several ACARS messages to Dispatch stating that I needed these numbers. They replied that the computer system wouldn't allow them to select A/I on with temps above 10C. I said that something needed to be done because our landing numbers will differ from those without engine A\I on. Also as a reminder the MEL states that the override switch must remain in the ENG position for the entirety of the flight in all phases.I looked at the QRH to see if there was a performance chart that could be utilized to derive a landing distance and weight for the above condition. There wasn't one. I then reviewed the QRH procedures to see if there was a factor to apply to an unfactored distance. There wasn't one.In this time I coordinated with ATC for some delay vectors so that we could formulate a plan. Our fuel was about 800 pounds over divert. I mentioned to Dispatch that we needed some numbers sooner than later and they replied that they were working to produce them. I informed ATC that we wanted to slow to 210 kts to save some fuel while we waited. They were happy to help with providing vectors just south of ZZZ. A short while later we heard back from Dispatch that there were no weight limits for Runway XXR for our configuration using flaps 45. We then noted that our fuel was showing 3;900 lbs over Runway XXR (Divert fuel was 3;881 lbs). We told ATC that we were ready for the approach. He vectored us to the approach and at this time we noticed that we were going to dip below divert (flight time remaining was about 6 minutes to the airport). Speed control in the descents played a part in the extra fuel used due to increased idle N2 settings with A/I on. Flaps were extended earlier than normal to aid in these speed and altitude changes. Upon landing we had 3;660 lbs of fuel which was well above our final divert of 3;188. After arriving at the gate I immediately called Dispatch to discuss the situation. I asked how the numbers were derived and I was told that they told the computer that the temp was 10C to eliminate the messages. The temperature in ZZZ was 15C and our next trip was to ZZZ1 where the temp was 33C. I said that this wasn't a good solution because of the effects of temperature on performance. I then said that I was going to ask for a different aircraft since; at this time; there was no way to produce accurate landing numbers. A different aircraft was provided for the remainder of the flights.I also called my Chief Pilot to discuss the situation. I was asked if I planned to [report] the event and I confirmed that I was. The Chief Pilot then called me back to say that he discussed the situation with another manager who said that it seems like this might be a limitation with the software. I mentioned that the MEL shouldn't be used if there was such a limitation in the planning software.There seems that there were several chances for this event to be averted. However it was missed in the planning and implementation phases. I usually verify the headers and notes on the TLR but this time I overlooked the landing notes. It wasn't until I noticed that the ACARS didn't want to provide info that I began digging deeper. Here is where I began the conversation with Dispatch. We were very focused on our fuel to ensure that we had adequate supply. It was my intention to ensure the safe operation of the aircraft; as always. Thus the request for delay vectors from ATC while we waited for numbers from Dispatch. I'm always trying to operate the aircraft by the book! However; in this case I missed my mark. I feel that we managed the situation the best that we could under the given circumstances. I must say that It was a frustrating situation; but one where I've learned.Hopefully this event will shed some light on what seems like a software limitation that is critical in complying with the MEL. I also hope that this [report]; while embarrassing and frustrating; will shed some light on an overlooked part of one MEL that can become more common as winter approaches.




Synopsis: EMB-145 Captain reported during MEL operation; computer software was unable to compute landing performance for given conditions.