Glossary
========

Terms as used in the HyFlux codebase and this documentation.

.. glossary::

   ASK
      Available seat-kilometre — seats offered × distance flown. The cost
      comparison reports per-ASK figures (``computeASK``).

   ATK
      Available tonne-kilometre — payload capacity × distance flown.

   ATJ
      Alcohol-to-jet — SAF pathway converting alcohols to jet fuel
      (feedstock category SS, CI 32.8 gCO₂e/MJ default).

   BAU
      Business as usual — the gross emissions trajectory with no
      decarbonisation wedges applied.

   BOR
      Boil-off recovery — fraction :math:`f_{BOR}` of evaporated hydrogen
      recaptured rather than vented (``bor``, default 50 %).

   CAGR
      Compound annual growth rate — traffic growth input (default
      3.5 %/yr); multi-segment via ``cagrPeriods``.

   CGI
      Custom Global Initiative — long-horizon CORSIA extension to 2100;
      implemented per DL-044 (``cgi_enabled``, ``cgi_gamma_end``;
      constrained offset mode only — :doc:`trafficGrowth`,
      :doc:`carbonOffsetsRemovals`).

   CI
      Carbon intensity — life-cycle emissions per unit fuel energy,
      gCO₂e/MJ (WTW unless stated).

   CORSIA
      Carbon Offsetting and Reduction Scheme for International Aviation —
      ICAO scheme; the sectoral subset (SEB/SGF) runs in production, and
      operator-level accounting (OEB/OGF/w(t)) is implemented standalone
      (:doc:`carbonOffsetsRemovals`).

   DAC / DACCS
      Direct air capture (and storage) — removal pathway and CO₂ source
      for PtL/PtG fuels; default capacity 5,000 MtCO₂/yr at 2050.

   DL
      Decision-log entry — ``ENGINEERING_DECISION_LOG.md`` provenance
      record (platform series DL-001…DL-164; the v5 publication series
      V5-DL-061… is logged separately in ``docs/decision-log-v5.md``).

   EIS
      Entry into service — first year a future aircraft type operates;
      internally decremented (:math:`t_{EIS} = t^*_{EIS} - 1`).

   EJ
      Exajoule — 10¹⁸ J; the energy-demand roll-up's unit.

   FAO
      Fleet & Airport Operations — operations efficiency category
      (ambition 0.8–4.0 %).

   FOG
      Fats, oils and greases — SAF feedstock category (HEFA-UCO, CI 13.9
      gCO₂e/MJ default).

   FT
      Fischer–Tropsch — synthesis converting CO/H₂ to liquid hydrocarbons;
      basis of FT-SAF and the PtL pathways.

   GH2
      Gaseous hydrogen — PtL/PtG feedstock form, tracked separately from
      LH₂ aircraft fuel (no liquefaction/boil-off terms).

   GWP100
      Global warming potential over 100 years — H₂ ≈ 11.6, CH₄ ≈ 29.8
      (claim register BC-12; citation attribution recorded as an open
      evidence gap :cite:`sand2023`).

   HEFA
      Hydroprocessed esters and fatty acids — leading near-term SAF
      pathway (HEFA-UCO).

   HTS / SC
      High-temperature superconducting — motor technology lever (``sc``)
      in HyFlux's extension analysis.

   JGE
      Jet-gallon-equivalent — 0.131354 GJ; the cost module's per-gallon
      normalisation.

   LCAF
      Lower-carbon aviation fuel — fossil jet with reduced upstream
      emissions (CI 65 gCO₂e/MJ default).

   LF
      Load factor — share of seats (or payload) filled; energy multiplier
      via RPTK conservation (:doc:`operations`).

   LH2
      Liquid hydrogen — cryogenic aircraft fuel; delivered CI includes
      liquefaction, vapor loss and boil-off recovery.

   LHV
      Lower heating value — energy basis throughout (Jet-A 43.2, H₂ 120,
      CH₄ 50 MJ/kg).

   MACC
      Marginal abatement cost curve — per-strategy marginal abatement
      cost :math:`MAC_{stype}` is implemented in the standalone CASCADE
      cost model (``cost-model.ts``, DL-134); the production economics
      block still reports per-pathway removal cost/capacity pairs and
      the blended average (:doc:`costs`).

   NEC
      Non-edible crops — SAF feedstock category (FT-Miscanthus, CI 20.2
      gCO₂e/MJ default).

   OGF
      Operator Growth Factor — CORSIA operator-level accounting term;
      implemented standalone with OEB, the w(t) schedule and the CGI
      operator analogues (``routes/corsia-operator.ts``,
      ``corsia-aggregation.ts``; DL-045/046/137) — not wired into the
      production sweep, operator set synthetic
      (:doc:`carbonOffsetsRemovals`).

   PtG
      Power-to-gas — e-methane synthesis (CO₂ + 4H₂ → CH₄ + 2H₂O);
      pathway added DL-032.

   PtL
      Power-to-liquid — e-fuel jet pathway (electrolysis + RWGS + FT);
      CI tracks electricity and GH₂ carbon intensity (DL-024).

   RNG
      Renewable natural gas — bio-methane from waste biogas (WTW CI 22
      gCO₂e/MJ default).

   RPTK
      Revenue passenger tonne-kilometre — payload traffic conserved by
      the load-factor formulation.

   RTK
      Revenue tonne-kilometre — total revenue payload traffic.

   RWGS
      Reverse water-gas shift — CO₂ + H₂ → CO + H₂O; first step of PtL
      synthesis.

   SAF
      Sustainable aviation fuel — drop-in jet fuels blended per
      feedstock (:doc:`energy`).

   SEB
      Sectoral Emissions Baseline — CORSIA baseline, 0.85 × 2019 sector
      emissions.

   SGF
      Sectoral Growth Factor — CORSIA offset share
      :math:`\max(0, (G - SEB)/G)`.

   SMR
      Steam methane reforming — fossil hydrogen production
      (:math:`CI_{SMR} = 0.045\,CI_{elec} + 85.95`).

   SS
      Sugars and starches — SAF feedstock category (ATJ).

   TTW
      Tank-to-wake — combustion-only emissions (Jet-A1 74 gCO₂e/MJ).

   WAR
      Wastes and residues — SAF feedstock category (FT-MSW, CI 28.4
      gCO₂e/MJ default).

   WTW
      Well-to-wake — full life-cycle emissions (Jet-A1 89 gCO₂e/MJ);
      the engine's canonical basis.