Date: 201908
Local time of day: 1801-2400
Location: ZZZ.TRACON, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
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: Fatigue
Anomaly: Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown; Inflight Event / Encounter Unstabilized Approach
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented
Contributing factors: Company Policy; Staffing
Primary problem: Ambiguous

Narrative: I am on short call reserve. Frequently; I am scheduled out to [reserve] because this is allowed per CFR 117 and our CBA. On this trip I was scheduled to fly [to] ZZZ; blocking in 14:40 minutes after my [Reserve] started; and 17:40 after I woke up for the day. Although I don't agree that this flavor of scheduling is smart or safety conscious; it's a frequent occurrence for me; and it's not realistic that I'm going to call in fatigued every time Crew Scheduling gives me a fatiguing assignment. If that were the case; I'd be calling in fatigued every week.Anyhow; on approach in ZZZ I was so tired I forgot to arm APP mode when cleared for the ILS 28C and couldn't figure out why I wasn't tracking the glide slope.  I was in LOC and LVL CHG; but didn't notice that error.  I couldn't figure out why my flight guidance on my PFD or in the HUD wasn't working as intended. I finally flipped up the HUD and turned off my FD. The entire approach; I was porpoising through the glide slope; first high; then low; then high; then low; etc…; and I couldn't figure out why because I was so tired. I think the approach technically met the stabilized criteria; but I honestly don't remember I was so fatigued. Once I cleared the runway; I didn't understand the taxi instructions and almost turned the wrong way.The last [XX] months on reserve have been a constant uphill against poor and unsafe scheduling; combating chronic and cumulative fatigue; and a corporate culture that pretends to put safety above all else; yet consistently demonstrates to our reserve pilots that this isn't the case.  No level of threat and error management or good CRM can trap all the schedule related threats being thrown my way or the way of all of our reserve pilots. Positive; safety conscious scheduling policies and procedures could however mitigate most of these threats. Sadly; that isn't the culture at our airline presently. Frankly; I've been lucky for the last [XX] months. As I saw in ZZZ the other night; my luck has finite limits.  All of our luck has limits. I'm afraid that if this level of unsafe and fatiguing scheduling keeps up for our reserve pilots; an aircraft incident or accident is on our near horizon. See abovePut in place fatigue mitigation rules for our pilots on reserve.




Synopsis: Air carrier pilot was flying an ILS approach in the wrong flight mode and did not understand why. Pilot described fatigue as the primary concern; regarding scheduling of reserve pilots.